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.

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

The ounce, the pound, and the ton are units of  
 (A) time. (B) weight. (C) length. (D) distance.
B

The invention of the microscope was important to the advancement of science. Many other discoveries were only possible with the help of the microscope. The microscope was used to make which discovery?  
 (A) Matter is made of elements. (B) Plants can make their own food. (C) Some organisms have only one cell. (D) White light can be broken into colors.

C