https://www.bis.org/publ/bcbs85.pdf - page 12
Banks should gather sufficient information about their respondent banks to understand fully the nature of the respondent's business. Factors to consider include: information about the respondent bank's management, major business activities, where they are located and its money-laundering prevention and detection efforts; the purpose of the account; the identity of any third party entities that will use the correspondent banking services; and the condition of bank regulation and supervision in the respondent's country. Banks should only establish correspondent relationships with foreign banks that are effectively supervised by the relevant authorities. For their part, respondent banks should have effective customer acceptance and KYC policies.

According to the CAMS Study Guide, page 191, "Reloadable open-loop prepaid cards are a high-risk product for money laundering because they can be used to store and move large amounts of funds anonymously. They can also be used to access cash at ATMs or through cash-back transactions at merchants." Therefore, option B is a red flag that may indicate money laundering, as a non-bank customer who regularly loads large amounts of cash onto several prepaid cards may be trying to avoid identification, verification, or transaction reporting requirements.
References:
CAMS Study Guide, page 1911

Enhanced due diligence (EDD) is a higher level of customer due diligence that is required for customers or accounts that pose a higher risk of money laundering or terrorist financing. According to the FATF Recommendations, EDD measures may include obtaining additional information on the customer, the beneficial owner, the intended nature and purpose of the business relationship, the source and destination of funds, and the reasons for transactions. EDD is also required for customers or accounts that are from or in countries that do not have adequate AML/CFT systems or are subject to sanctions or embargoes.
Among the four categories of customers or accounts listed in the question, lawyers, foreign exchange dealers, and precious metal dealers are considered as high-risk by the FATF and other international standards, and therefore require EDD. Lawyers may be involved in transactions that conceal the origin or ownership of illicit funds, such as creating shell companies, trusts, or foundations. Foreign exchange dealers may facilitate the movement of illicit funds across borders or jurisdictions, or provide anonymous or pseudonymous services.
Precious metal dealers may deal with high-value goods that are easily convertible into cash, or may be used to launder proceeds of crime or evade sanctions.
Retail account holders, on the other hand, are generally considered as low-risk customers or accounts, unless they exhibit unusual or suspicious behavior or transactions. Therefore, they do not require EDD by default, but only when there are specific indicators of higher risk.
References:
[ACAMS Study Guide for the CAMS Certification Examination, 6th Edition], Chapter 3: Compliance Standards for Anti-Money Laundering (AML) and Combating the Financing of Terrorism (CFT), pp.
75-76, 79-80.
FATF Guidance on Correspondent Banking Services, October 2016, pp. 7-8, 12-13.
Customer Due Diligence - Overview, Federal Financial Institutions Examination Council, April 2018, pp. 1-2, 5-6.
Customer due diligence, The Law Society, accessed on February 9, 2024.
Anti-Money Laundering (AML) Source Tool for Broker-Dealers, U.S. Securities and Exchange Commission, May 16, 2022, pp. 1-2, 5-6.