Mutual Legal Assistance Treaties (MLATs) are characteristics of D. only involving two countries, E.
cooperatively combating crime between countries, and F. being useful for gathering evidence and intelligence in a foreign country. MLATs are public and binding under international law (A), can be used for obtaining banking records from treaty partners (B), and provide a legal basis for transmitting evidence .

According to the ACAMS Study Guide 6th Edition, Chapter 2, page 36, one of the methods that financial institutions can use to identify suspicious or unusual activity is to monitor transactions for red flags or indicators of money laundering or terrorist financing. Some of the common red flags are:
Transactions that are inconsistent with the customer's profile, business, or source of funds Transactions that involve high-risk countries or jurisdictions, especially those with weak or inadequate anti-money laundering regulations, or those known to be sources or destinations of illicit funds Transactions that involve the use of complex or unusual financial instruments or structures, such as multiple accounts, intermediaries, or offshore entities, that have no apparent economic or lawful purpose Transactions that involve the use of large amounts of cash, checks, or monetary instruments, especially if they are structured or aggregated to avoid reporting or recordkeeping requirements Transactions that involve the use of third parties or nominees, such as relatives, associates, or shell companies, to conceal the identity, ownership, or control of the funds or assets Option B is a transaction type that warrants investigation, as it involves sending large number of high dollar international wires to different countries, which could indicate that the customer is involved in layering or integration stages of money laundering, where the illicit funds are moved across borders and disguised as legitimate transfers. This transaction type also raises the risk of exposure to sanctions, terrorist financing, or other illicit activities, depending on the destination and purpose of the wires.
Option D is also a transaction type that warrants investigation, as it involves depositing a lot of checks drawn on banks in foreign countries, which could indicate that the customer is involved in placement or layering stages of money laundering, where the illicit funds are introduced into the financial system or converted into other forms of value. This transaction type also raises the risk of exposure to fraud, counterfeit, or forgery, depending on the origin and authenticity of the checks.
Option A is not a transaction type that warrants investigation, as it involves making regular cash deposits of a few hundred dollars every few days, which could be consistent with the customer's profile, business, or source of funds, especially if the customer is an ice cream vendor who operates in cash. This transaction type does not raise any red flags of money laundering or terrorist financing, unless there is evidence that the cash deposits are structured or aggregated to avoid reporting or recordkeeping requirements.
Option C is also not a transaction type that warrants investigation, as it involves writing multiple checks for a few hundred dollars to the same dozen payees every two weeks, which could be consistent with the customer's profile, business, or source of funds, especially if the payees are suppliers, employees, or contractors of the customer. This transaction type does not raise any red flags of money laundering or terrorist financing, unless there is evidence that the checks are used to facilitate illicit activities, such as bribery, kickbacks, or tax evasion.
References:
ACAMS Study Guide 6th Edition, Chapter 2, page 36
Red Flags And Atypical Customer Behavior: Anti-Money Laundering Awareness
4 Red Flags of Money Laundering or Terrorist Financing

The customer activity that poses the highest risk of money laundering is making multiple cash deposits slightly below a required reporting limit. This could indicate a practice known as structuring or smurfing, which is a method of breaking down large amounts of cash into smaller transactions to avoid detection or reporting by financial institutions12. Structuring is a common technique used by money launderers to conceal the source, ownership, or destination of illicit funds3.
The other options are not necessarily indicative of money laundering, although they may require further due diligence or monitoring depending on the customer profile and the nature of the transaction. For example:
Transferring funds to pay for flight training lessons could be a legitimate educational expense, or it could be related to terrorist financing or other criminal activities. The financial institution should verify the identity and background of the customer and the recipient, and check for any red flags or suspicious indicators4.
Paying a supplier of precious metals at regular quarterly intervals could be a normal business practice, or it could be a way of moving or storing value in an alternative asset class. The financial institution should assess the customer's source of funds, business rationale, and market conditions, and monitor for any changes or inconsistencies.
Conducting business in a country that represents a high risk of money laundering could be a legitimate commercial opportunity, or it could be a sign of involvement in illicit activities or tax evasion. The financial institution should apply enhanced due diligence measures, such as verifying the identity and reputation of the customer and the counterparties, obtaining information on the purpose and nature of the business relationship, and screening for any sanctions or adverse media.
References:
ACAMS CAMS Certification Video Training Course - Exam-Labs3
Exam CAMS: Certified Anti-Money Laundering Specialist (the 6th edition)4 ACAMS Study Guide for the Certification Examination, 6th Edition, Chapter 2, page 29:
https://www.acams.org/wp-content/uploads/2019/08/ACAMS-Study-Guide-6th-Edition-Chapter-2.pdf ACAMS Study Guide for the Certification Examination, 6th Edition, Chapter 6, page 121:
https://www.acams.org/wp-content/uploads/2019/08/ACAMS-Study-Guide-6th-Edition-Chapter-6.pdf ACAMS Study Guide for the Certification Examination, 6th Edition, Chapter 7, page 139:
https://www.acams.org/wp-content/uploads/2019/08/ACAMS-Study-Guide-6th-Edition-Chapter-7.pdf ACAMS Study Guide for the Certification Examination, 6th Edition, Chapter 4, page 77:
https://www.acams.org/wp-content/uploads/2019/08/ACAMS-Study-Guide-6th-Edition-Chapter-4.pdf

According to the Basel Committee on Banking Supervision (BCBS), a sound KYC program should contain four essential elements: (i) customer acceptance policy; (ii) customer identification; (iii) on-going monitoring of higher risk accounts; and (iv) risk management1. These elements correspond to the options B in the question, as customer identification involves verifying the identity and beneficial ownership of the customers, risk assessment involves determining the level of risk posed by the customers and their activities, customer screening involves checking the customers against relevant sanctions and watch lists, and monitoring involves reviewing the customers' transactions and behavior for any anomalies or red flags.
References:
Consolidated KYC Risk Management - Bank for International Settlements
Reference: https://www.bis.org/publ/bcbs77.pdf

Structured transactions are a common method of money laundering, where large amounts of cash are broken down into smaller deposits or withdrawals to avoid reporting thresholds or detection. The most effective tool to detect such transactions is a software program that can link apparently unrelated transactions by using various criteria, such as customer name, address, account number, identification number, transaction amount, date, time, location, etc. Such a program can help identify patterns, trends, and anomalies that may indicate money laundering activity.
References:
ACAMS CAMS Certification Study Guide1, Chapter 2: Money Laundering Risks and Methods, Section
2.2: Common Money Laundering Methods, pp. 51-52
ACAMS CAMS Certification Video Training Course2, Module 2: Money Laundering Risks and Methods, Lesson 2.2: Common Money Laundering Methods ACAMS CAMS Certification Exam Outline3, Domain 2: Compliance Standards for Anti-Money Laundering (AML) and Combating the Financing of Terrorism (CFT), Task 2.2: Implement risk-based CDD, EDD and ongoing due diligence policies, procedures and processes, p. 13