instruction:
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.
question:
Many scientists are convinced that an increase of certain gases in the atmosphere is affecting global temperatures. What makes this hypothesis difficult to prove?  
 (A) Trees absorb these gases. (B) Global temperatures are rising. (C) Many variables affect global temperatures. (D) Many human activities produce these gases.
answer:
C


question:
As water cools to a temperature of zero degrees Celsius and forms ice, water molecules tend to  
 (A) move farther apart. (B) vibrate rapidly. (C) flow more randomly. (D) gradually expand.
answer:
A


question:
Claudia's teacher places a photograph of an organism on the board. He asks Claudia to determine if the organism is a plant or an animal. The answer to which question will best help Claudia determine if the organism is a plant or an animal?  
 (A) Does the organism have cells? (B) Does the organism reproduce? (C) Does the organism live in the forest? (D) Does the organism make its own food?
answer:

D