According to the ACAMS study guide, one of the training elements that should be delivered to new tellers during employee orientation is "large cash transaction reporting procedures" (p. 224). This is because tellers are often the first line of defense against money laundering and have the responsibility to identify and report any transactions that exceed the threshold of $10,000 or are otherwise suspicious. The other options are not relevant for tellers, as they are more suitable for higher-level or specialized staff.
References:
ACAMS. (2020). Study Guide for the Certification Examination for Anti-Money Laundering Specialists (6th ed.). Miami, FL: ACAMS.
AML Requirements for Tellers 1
Deposit Compliance Training Courses 2
As the compliance officer is providing overview of the "bank's anti-money laundering program to a group of new tellers during employee orientation"

This is stated in the Certified Anti-Money Laundering Specialist (the 6th edition) manual on page 595, which states: "Potential indicators of money laundering associated with Trust and Company Service Providers include the use of legal persons in jurisdictions with strict secrecy laws, structuring cash deposits into third party accounts, multi-jurisdictional wire transfers with no legal purpose, and frequent deposits to or withdrawals from bank accounts."

The specialist should recommend directing the teller (cashier) to file a suspicious transaction report (STR). This is because the teller (cashier) has failed to comply with the bank's internal policies and procedures for reporting unusual or suspicious activity, which is a key component of an effective anti-money laundering (AML) program1. The teller (cashier) should have filed an internal report of unusual activity as soon as he or she noticed the suspicious transactions, regardless of the personal circumstances or the length of service of the customer involved2. Failing to do so could expose the bank to regulatory sanctions, reputational damage, or legal liability3.
The other options are not appropriate recommendations for the specialist to make in this situation. Continuing to monitor the accounts is not sufficient, as it does not address the past non-compliance or the potential money laundering risk posed by the suspicious transactions. Refreshing anti-money laundering training for the teller (cashier) is not enough, as it does not ensure that the teller (cashier) will report the suspicious transactions or prevent future violations. Suspending the teller's (cashier's) employment is too harsh, as it does not take into account the teller's (cashier's) long and exemplary work record, the personal hardship faced by the teller's (cashier's) family, or the possibility of remedial actions or corrective measures4.
References:
1: Internal Controls | FinCEN.gov1 2: Reporting Suspicious Transactions - ACAMS2 3: The Consequences of Non-Compliance with AML Regulations - Blog | Unit213 4: Employee Discipline in the Workplace: A Guide for Managers4