The important fact to include in the STR is the recent change in the timing of deposits and withdrawals in the account, as this indicates a possible change in the customer's source and use of funds, and may suggest money laundering or other illicit activity. The customer's work history, the amount of his monthly retirement check, the fact that he is well known to the bank staff, and the fact that he has lived in the area and banked at this bank for 25 years are not relevant for the STR, as they do not explain the unusual pattern of transactions in his account.
References:
CAMS Certification Package - 6th Edition | ACAMS, Chapter 4: Conducting and Supporting the Investigation Process, page 131 CAMS Certifications: How to Get CAMS Certified | ACAMS, CAMS Examination Preparation, page 8 ACAMS CAMS Certification Video Training Course - Exam-Labs, Video 4.2: Suspicious Transaction Reporting Exam CAMS: Certified Anti-Money Laundering Specialist (the 6th edition), Question 97

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

A compliance officer should consider the following three factors as part of the approach to implement an enterprise-wide anti-money laundering program for a bank that operates in multiple countries:
The types of customers serviced by the bank: Different types of customers may pose different levels of money laundering risk, depending on their nature, source of funds, geographic location, transaction patterns, and other factors. A compliance officer should identify and assess the money laundering risk associated with each customer type and segment, and apply appropriate due diligence measures, monitoring systems, and risk mitigation strategies accordingly12.
The extent of anti-money laundering regulations in the various countries: A compliance officer should be aware of the legal and regulatory requirements and expectations for anti-money laundering compliance in each country where the bank operates, and ensure that the bank's policies and procedures are consistent with them. A compliance officer should also monitor any changes or updates in the anti-money laundering laws and regulations in the various countries, and adjust the bank's program accordingly34.
The anti-money laundering risk posed by the products and services offered by the bank: Different products and services may have different features and functionalities that could be exploited by money launderers, such as anonymity, cross-border transfers, cash transactions, complex structures, or new technologies. A compliance officer should evaluate the money laundering risk associated with each product and service offered by the bank, and implement appropriate controls, safeguards, and oversight mechanisms to prevent and detect money laundering activities5 .
References:
1: ACAMS, CAMS Study Guide, 6th Edition, Chapter 2: Risk Assessments
2: FATF, Guidance for a Risk-Based Approach: The Banking Sector
3: ACAMS, CAMS Study Guide, 6th Edition, Chapter 3: Compliance Standards for Anti-Money Laundering (AML) and Combating the Financing of Terrorism (CFT)
4: Deloitte, AML Program Effectiveness Reform
5: ACAMS, CAMS Study Guide, 6th Edition, Chapter 4: AML Program Design
[6]: OCC, Money Laundering: A Banker's Guide to Avoiding Problems