instruction:
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.
question:
Which substance is a compound?  
 (A) butter (B) nitrogen (C) hydrogen (D) ammonia
answer:
D


question:
Some plants produce fruit such as apples. What is one function of a fruit?  
 (A) to protect seeds (B) to produce food for seeds (C) to stop seeds from dispersing (D) to store water for seed germination
answer:
A


question:
Under which circumstance would an adaptation be useful that allows tadpoles to go through a shortened period of metamorphosis?  
 (A) when tadpoles need to swim immediately (B) when there is a limited amount of water in their environment (C) when there is a decrease in the number of predators (D) when tadpoles need to blend in with their surroundings
answer:

B