In this task, you are given two facts, and a multiple-choice question. Based on the given facts, answer the question with index of the correct option (e.g, "A").

Fact1: Mammals generate heat mainly by keeping their metabolic rate high., Fact2: Gray Squirrel Management Tree squirrels are common Alabama mammals., Question: What generate heat mainly by keeping their metabolic rate high? (A) elephants (B) fur seals (C) bacteria (D) alpacas (E) tree squirrels (F) animals (G) batteries (H) the Sun
E