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.

Ex Input:
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

Ex Output:
A


Ex Input:
Many horses grow a heavy coat in autumn and shed that coat in spring. Scientists were not sure if temperature or the amount of daylight per day (called the photoperiod) caused the change. So, they conducted an experiment and concluded that the change in photoperiod was responsible for the biological changes. Shedding caused by which set of conditions would have helped them arrive at this conclusion?  
 (A) a constant photoperiod, but varied temperatures (B) a varied photoperiod, and varied temperatures (C) a constant photoperiod, and a constant temperature (D) a varied photoperiod, but a constant temperature

Ex Output:
D


Ex Input:
A student measures the acceleration of a stone block on a level surface when the block is acted upon by a known force. What additional information is needed to precisely calculate the block's mass?  
 (A) the block's density (B) the amount of friction (C) the mass of the surface (D) the direction of motion

Ex Output:

B