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.

Ex Input:
Some scientists have suggested that the Moon was formed when a large body struck Earth and broke off a piece of Earth billions of years ago. Which observation would best support this suggestion?  
 (A) The rocks of the Moon are older than Earth rocks. (B) The Earth has free standing water, but the Moon does not. (C) The Earth and the Moon are gravitationally locked together. (D) The chemical composition of Moon rocks is similar to Earth rocks.

Ex Output:
D


Ex Input:
Which of these technologies helps a power company use renewable energy for the production of electricity?  
 (A) hydroelectric power (B) nuclear power plants (C) natural gas generators (D) coal-fired power plants

Ex Output:
A


Ex Input:
Greenhouse gases in the atmosphere trap heat near Earth's surface. Which of these is a greenhouse gas?  
 (A) nitrogen (B) argon (C) water vapor (D) oxygen

Ex Output:

C