instruction:
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.
question:
Which of the following would be more likely to pollute a river?  
 (A) allowing beavers to build a dam (B) spreading fertilizer near the river (C) mowing the grass on the river bank (D) fishing from a bridge over the river
answer:
B


question:
Which is an example of a form of electrical energy?  
 (A) lightning (B) windmill (C) radio waves (D) sound waves
answer:
A


question:
What happens to metal railroad tracks during the heat of a summer day?  
 (A) decrease in weight (B) increase in weight (C) decrease in length (D) increase in length
answer:

D