According to the CAMS Certification Package - 6th Edition1, a financial institution that processes a wire transfer is required to file a suspicious transaction report (STR) in the jurisdiction where it is located, if it detects any red flags or indicators of money laundering, terrorism financing, or other financial crimes. The financial institution does not need to file an STR in the jurisdictions of the originator or the beneficiary of the wire transfer, unless it has a branch or a subsidiary there. Therefore, the correct answer is A. The transaction in Country A.
References:
* CAMS Certification Package - 6th Edition1, Chapter 4: Compliance Standards for Anti-Money Laundering (AML) and Combating the Financing of Terrorism (CFT), Section: Wire Transfers, pp. 161-
162.