TASK DEFINITION: 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.
PROBLEM: A student notices a paw print while walking in a park. The paw print could be considered a fossil if the print was in ___.  
 (A) rock (B) topsoil (C) thick mud (D) loose sand

SOLUTION: A

PROBLEM: In the human body, which system functions primarily to defend the body against disease?  
 (A) digestive (B) immune (C) nervous (D) respiratory

SOLUTION: B

PROBLEM: Which best explains why some reptiles and amphibians lay an abundance of eggs?  
 (A) It increases the population. (B) The eggs provide food for predators. (C) These animals do not have to stay with their eggs. (D) It increases the chance of some eggs surviving to hatch.

SOLUTION:
D