Teacher: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.
Teacher: Now, understand the problem? Solve this instance: A donkey and a horse can be bred to produce a mule. Which observation is evidence that donkeys and horses are two different species?
(A) They have different body sizes. (B) A mule is not able to reproduce. (C) They are found in different environments. (D) A mule does not resemble either parent.
Student:
B