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.

When a hammer strikes a nail, the nail  
 (A) exerts balanced forces that helps it from moving. (B) exerts a force equal to the weight of the hammer. (C) exerts an unbalanced force that changes its velocity. (D) exerts an equal and opposite force back on the hammer.
D

What is a main feature of plains?  
 (A) a flat, level surface (B) a high, steep peak (C) a low, shallow basin (D) a gentle, gradual slope
A

Deer provide food for wolves. How does this relationship also benefit the deer herd?  
 (A) by protecting deer from other predators (B) by controlling the deer population (C) by decreasing diversity within the herd (D) by protecting the deer from disease

B