Implementing a sound customer due diligence (CDD) program is the most effective way to prevent money laundering through financial institutions, according to experts. CDD is the process of identifying and verifying the identity of customers and assessing their risk profile, source of funds, and expected activity. CDD helps financial institutions to detect and prevent money laundering by enabling them to know their customers, monitor their transactions, and report any suspicious or unusual behavior. CDD is also a key requirement of the international standards and best practices for anti-money laundering and combating the financing of terrorism (AML/CFT), such as the Financial Action Task Force (FATF) Recommendations and the Basel Committee on Banking Supervision (BCBS) Guidelines.
The other options are not as effective as CDD, as they are either too narrow or too broad in scope. Ensuring that transaction monitoring systems can identify terrorist financing is important, but it does not address the broader issue of money laundering, which may involve other types of criminal proceeds or activities.
Collecting information on beneficial owners and foreign customers is a part of CDD, but it is not sufficient by itself, as it does not cover the risk assessment and ongoing monitoring aspects of CDD. Instituting a policy prohibiting the acceptance of funds intended for terrorist financing is a good practice, but it is not a preventive measure, as it relies on the assumption that the funds are already identified as such, which may not be the case.
References:
Customer Due Diligence - FATF-GAFI.ORG
Sound management of risks related to money laundering and financing of terrorism - Bank for International Settlements CAMS Study Guide 6th Edition, page 36-37.

According to the Financial Action Task Force (FATF) Special Recommendation IV, if financial institutions, or other businesses or entities subject to anti-money laundering obligations, suspect or have reasonable grounds to suspect that funds are linked or related to, or are to be used for terrorism, terrorist acts or by terrorist organisations, they should be required to report promptly their suspicions to the competent authorities1. This is consistent with the FATF Recommendation 20, which requires the same reporting obligation for money laundering and the financing of proliferation of weapons of mass destruction2.
Reporting suspicious transactions related to terrorism is a key measure to detect, prevent and suppress the financing of terrorism and terrorist acts, and to facilitate international cooperation and information exchange.
References:
* 1: The FATF Recommendations - Financial Action Task Force
* 2: IX Special Recommendations - Financial Action Task Force

Using cash to buy multiple cashier's checks over a period of time is considered suspicious activity of money laundering. This method is commonly known as structuring, where individuals or entities use cash to buy multiple monetary instruments such as cashier's checks in small amounts, to avoid reporting requirements.
This behavior could be an attempt to evade transaction monitoring and reporting requirements by a financial institution. Additionally, the fact that the account also receives multiple electronic transfers for the same amount could be a red flag for money laundering as it is a common technique used to layer or disguise the origin of illicit funds.
Reference: Certified Anti-Money Laundering Specialist (the 6th edition) Study Guide, page 100-101.