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.

Some people carry a mutated allele of a particular gene that makes them resistant to HIV infection and AIDS. Which best describes this type of mutation?  
 (A) beneficial (B) asexual (C) harmful (D) unicellular
A

Auroras occur where Earth's magnetosphere traps high-energy particles in which region of the atmosphere?  
 (A) troposphere (B) stratosphere (C) thermosphere (D) exosphere
C

The muscles exert forces on the body and enable movement by  
 (A) pushing on tendons. (B) squeezing ligaments. (C) stimulating the spinal cord. (D) pulling on bones.

D