You will be given a definition of a task first, then some input of the task.
You are given a science question (hard-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.

Which of these is the main function of the vomiting reflex?  
 (A) to rid the body of wastes (B) to expel food that has no nutritional value (C) to empty the stomach when it has too much food in it (D) to remove toxic material from the stomach before it is absorbed
Output:
D