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]: Which type of air mass forms over the ocean near the equator?  
 (A) moist and warm (B) moist and cool (C) dry and warm (D) dry and cool
[EX A]: A

[EX Q]: Which of the following compounds is most likely to be part of living organisms?  
 (A) C?H??O? (B) BF? (C) MoCl? (D) CsI
[EX A]: A

[EX Q]: Which of the following structures does a frog develop as it changes from a tadpole to an adult frog?  
 (A) eyes (B) heart (C) lungs (D) tail
[EX A]:
C