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 of these cycles takes 24 hours?  
 (A) Earth rotating on its axis (B) Earth revolving around the Sun (C) the Moon rotating on its axis (D) the Moon revolving around Earth
[EX A]: A

[EX Q]: Fertilizers can enable farmers to grow the same crop in a field for several years in a row. Farmers who use less fertilizer often rotate their crops by planting the crop one year and legumes, such as beans and clover, the following year. Fertilizer use and crop rotation with legumes both increase the availability of which of the following nutrients in soil?  
 (A) calcium (B) nitrogen (C) oxygen (D) protein
[EX A]: B

[EX Q]: What is the most likely reason the giant sloth became extinct in North America and Cuba?  
 (A) disease (B) loss of habitat (C) climate change (D) humans as predators
[EX A]:
D