Hi, let's look at the argument. The author tells us in the first sentence that great jazz singers emulate horns, and the second sentence is an example supporting the first sentence. The third sentence tells us that the opposite is true as well, horn players emulate voices. The author then concludes that jazz is voices emulating horns and visa versa.
We are asked what the first sentence does. Since it supports the eventual conclusion in the final sentence, and is supported by the second sentence we know it's an intermediate conclusion, which matches C.
