Answer:
D. Ethos
Step-by-step explanation:
According to this passage from "The Obligation to Endure, the author talks about the insect problem, looking at it from a historical viewpoint. He mentions the work of Charles Elton, a British ecologist to back up his assertions.
The appeal(s) that Carson relies on most in this passage is Ethos. This is because, he makes use of historical evidence.