C. Social engineering
Explanation:
Social engineering is a manipulation technique that exploits human error to gain private information, access, or valuables. In this scenario, the suspicious caller was attempting to deceive the user into providing credit card information by falsely claiming to be acting on behalf of the Chief Financial Officer. This tactic is a classic example of social engineering, where the attacker uses social manipulation rather than technical hacking methods to obtain sensitive information.
It is not D because this is a type of phishing attack that specifically targets high-profile executives (also known as "whales") to steal sensitive information. While the scenario does involve the mention of a high-ranking executive, it is broader in scope and fits under the general category of social engineering rather than a specific whaling attack through email.