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 rubber band will make a sound when it is  
 (A) vibrated. (B) stretched. (C) cut into pieces. (D) shot across a room.

Ex Output:
A


Ex Input:
When nitrogen-rich runoff from farms enters a nearby farm, it causes abundant growth of algal mat on the pond surface. As a result, underwater plants in the pond begin to die. Identify the limiting factor that is most responsible for causing the underwater plants to die.  
 (A) oxygen (B) sunlight (C) nitrogen (D) carbon dioxide

Ex Output:
B


Ex Input:
Which organism is a producer?  
 (A) frog (B) mushroom (C) grass (D) lizard

Ex Output:

C