Given the task definition and input, reply with output. 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").

An example of combining two substances is (A) pouring queso into guacamole (B) setting a laptop on a desk (C) building a roof on a house (D) putting clothes in a suitcase
A