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 delta at the mouth of a river is the direct result of  
 (A) runoff from sewage. (B) deposition of sediment. (C) an ancient glacier that passed through. (D) an underground river flowing to the ocean.

Ex Output:
B


Ex Input:
When microorganisms deplete the oxygen in soil through respiration, the soil becomes  
 (A) humus. (B) anaerobic. (C) compost. (D) aerobic.

Ex Output:
B


Ex Input:
Many scientists think that when birds migrate to the same location each year, they find this location by using Earth's  
 (A) jet stream. (B) weather patterns. (C) magnetic patterns. (D) electrical discharges.

Ex Output:

C