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:
The main function of a fish's fins is to help the fish  
 (A) reproduce (B) see (C) breathe (D) move

Ex Output:
D


Ex Input:
Similar types of cells form tissues. What is the next level of complexity formed from the grouping of tissues?  
 (A) organs (B) organelles (C) organisms (D) organ systems

Ex Output:
A


Ex Input:
Which human organ system produces hormones to regulate growth, development, and reproduction?  
 (A) circulatory (B) digestive (C) nervous (D) endocrine

Ex Output:

D