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 Q]: 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.
[EX A]: C

[EX Q]: Which would be the best method to use to dispose of cardboard boxes not utilized by a local grocery store?  
 (A) burn them once a month (B) send them to be dumped in a remote area (C) have them recycled for future paper products (D) put them into a dumpster with the rest of the trash
[EX A]: C

[EX Q]: Frame construction predominates in the New England area due to the abundance of  
 (A) clay. (B) masonry. (C) wood. (D) steel.
[EX A]:
C