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.

Ex Input:
A bird eats a brightly-colored insect that tastes bad. The bird avoids preying on this type of insect again. This example is best described as  
 (A) a physical characteristic. (B) a learned behavior. (C) an inherited behavior. (D) an adaptation.

Ex Output:
B


Ex Input:
The shape of a riverbed changes over time as a result of which gradual process?  
 (A) erosion (B) dissolving (C) plate shifting (D) compaction

Ex Output:
A


Ex Input:
Proxima Centauri is the closest star to the Sun. Which units do astronomers most often use for the distance between Earth and Proxima Centauri?  
 (A) miles (B) meters (C) light years (D) astronomical units

Ex Output:

C