You are given a science question (easy-level) and four answer options (associated with "A", "B", "C", "D"). Your task is to find the correct answer based on scientific facts, knowledge, and reasoning. Do not generate anything else apart from one of the following characters: 'A', 'B, 'C', 'D'. There is only one correct answer for each question.

There are different kinds of muscles in the human body. Each muscle is formed from a group of cells that works together. The main function of a group of muscle cells is to
(A) make oxygen. (B) release energy. (C) digest nutrients. (D) cause movement.
D