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 best describes a characteristic of the jet stream?  
 (A) It forms a boundary between a cold air mass and a warm air mass. (B) It creates the high winds around the eye of a hurricane. (C) It forces the hot air along the equator to rise to areas in North America. (D) It causes high pressure air masses to rotate clockwise.
[EX A]: A

[EX Q]: Which of these elements is found in the greatest amount in organisms?  
 (A) carbon (B) iron (C) lead (D) neon
[EX A]: A

[EX Q]: Energy flows in an ecosystem through food webs. Which form of energy is the least available for reuse in a food web?  
 (A) heat energy (B) sunlight energy (C) energy from producers (D) energy from consumers
[EX A]:
A