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: preventing the transfer of heat from an organims 's body causes that organism to keep warm, Fact2: Radiation is the major method of heat transfer warming Bob's face., Question: what keeps humans warm? (A) Animal fur (B) Solar energy (C) wind (D) radiation (E) Evaporation (F) snow (G) magnets (H) exoskeleton
D