In this task, you are given a multiple-choice question and you have to pick the correct option. Answer with option indexes (i.e., "A", "B", "C", and "D").

Input: Consider Input: An echo is produced by what type of reflection of sound source? (A) Direct (B) Distant (C) Varied (D) Single

Output: D

Input: Consider Input: Greenhouses are great for plants like (A) Pizza (B) Lollipops (C) Candles (D) French beans

Output: D

Input: Consider Input: A thermal insulator slows the transfer of what? (A) warmness (B) light (C) energy (D) liquid
Output: A