Answer: A. Refusing to trade with a country until it improves its human rights record.
Explanation: The question asked about using economic influence as a tool of foreign policy. Trade and commerce are economic activities. Imposing trade sanctions against a country is a way of exercising economic influence. In this case, the economic influence is being used to try to achieve a foreign policy goal -- the recognition of universal human rights.
As for the other responses ...
- Sending troops would be the use of military (not economic) influence.
- Appointing an ambassador would be an exercise of diplomatic influence.
- Creating an alliance would also be a diplomatic or political measure (not an economic one).
