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.

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


[Q]: A radio station broadcasting across a large area is experiencing thunderstorms. How will the radio waves from the station be affected?  
 (A) wavelength will be increased (B) amplitude will be unchanged (C) frequency will be distorted (D) speed will be decreased
[A]: C


[Q]: How does sedimentary rock form?  
 (A) sediments cool (B) sediments melt (C) sediments separate (D) sediments compress
[A]:
D