The customer activity that should trigger a suspicious transaction report is purchasing travelers checks (cheques) for trips to a Non-Cooperative Countries and Territories (NCCTs). This could indicate an attempt to evade currency reporting requirements, avoid sanctions or embargoes, or facilitate money laundering or terrorist financing through high-risk jurisdictions12. NCCTs are countries or territories that have been identified by the Financial Action Task Force (FATF) as having serious deficiencies in their anti-money laundering and counter-terrorist financing regimes, and that pose a threat to the international financial system3.
The other options are not necessarily grounds for a suspicious transaction report, although they may require further due diligence or monitoring depending on the customer profile and the nature of the transaction. For example:
The increased activity is due to money order deposits. This could be a legitimate source of income for the customer's export business, or it could be a way of disguising the origin or destination of the funds. The anti-money laundering specialist should verify the identity and background of the customer and the issuers of the money orders, and check for any red flags or suspicious indicators4.
Wire transfers are coming from a Financial Action Task Force member country. This could be a normal business practice, or it could be a sign of involvement in trade-based money laundering or other illicit activities. The anti-money laundering specialist should assess the customer's source of funds, business rationale, and market conditions, and monitor for any changes or inconsistencies.
The client changed his address without advising the institution. This could be a simple oversight, or it could be a way of concealing the customer's true location or identity. The anti-money laundering specialist should update the customer's information, verify the new address, and check for any adverse media or sanctions.
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 1, page 11:
https://www.acams.org/wp-content/uploads/2019/08/ACAMS-Study-Guide-6th-Edition-Chapter-1.pdf 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 4, page 77:
https://www.acams.org/wp-content/uploads/2019/08/ACAMS-Study-Guide-6th-Edition-Chapter-4.pdf ACAMS Study Guide for the Certification Examination, 6th Edition, Chapter 5, page 97:
https://www.acams.org/wp-content/uploads/2019/08/ACAMS-Study-Guide-6th-Edition-Chapter-5.pdf

When investigating an AML event, the following techniques would be used to investigate suspected mule accounts:
A: Determine if the suspected accounts are being accessed by a common person, telephone number, or device. This can help identify if the accounts are controlled by the same person or group, or if they are part of a larger network of mules. It can also help detect if the accounts are opened using synthetic identities or stolen credentials12.
B: Reconcile the stated purpose of the account with actual transaction history and compare with peer groups. This can help assess if the account activity is consistent with the customer profile, risk rating, and expected behavior. It can also help identify anomalies, such as sudden changes in transaction patterns, large or frequent transfers, or transactions with high-risk jurisdictions or entities12.
E: Establish the frequency with which the funds are moved in and out of the accounts. This can help measure the velocity and volume of the funds flowing through the accounts, which can indicate if the accounts are used for layering or integration of illicit funds. It can also help detect if the accounts are used for smurfing, which is a technique of breaking down large amounts of cash into smaller deposits to avoid detection or reporting thresholds13.
References:
CAMS Study Guide (the 6th edition), page 1841
Mule accounts: how to track them down - Linkurious2
Money Mules - FBI3

Explanation