Hey there! I'm happy to help!
Proxy means that something is done representing something or someone else. If you tell somebody to say hi to someone for you, they are saying hi to that other person in proxy for you.
Answer B talks about sending spies. This has nothing to do with proxy.
Answer C talks about getting more weapons. This doesn't have anything to do with representation.
Answer D talks about engaging in direct military conflicts. If the US and USSR armies were fighting each other, that would not be proxy because there is no one else representing them.
Answer A talks about supporting armies in conflicts around the world. In Korea, the USSR supported North Korea and the US supported South Korea. These two fought kind of on behalf of the USSR and US, so it is basically proxy. North Korea represented the USSR and South Korea represented the US.
Therefore, the answer is A. supporting armies in conflicts around the world.
Have a wonderful day! :D
