Q: 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").
A man is building a cabin in a forested area that receives a lot of snow in the winter. The man would like the cabin to retain heat in the winter so that the cabin stays warm and that it is inexpensive to heat. In order to facilitate this desire, the man lines the walls of his cabin with (A) thermal insulator (B) glass (C) thermal gravity (D) hard plastic
A:
A