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:
Which of the following is an observation about grasshoppers that a science class could have made on their nature walk?
(A) The grasshoppers will live longest in a container filled with plants. (B) The grasshoppers are green with long back legs and antennae. (C) The grasshoppers will probably eat more grass than tree leaves. (D) The grasshoppers all hatched from eggs laid the year before.

Ex Output:
B

Ex Input:
Water in the solid phase has a crystal structure which keeps molecules farther apart than water at certain temperatures in the liquid phase. This relationship explains which property?
(A) the presence of more impurities in ice than in liquid water (B) the ability of ice to float on liquid water (C) the release of heat when liquid water turns into ice (D) the cooling of liquid water as it flows over ice

Ex Output:
B

Ex Input:
The nucleus of the cell controls cell activity. Which body system performs a similar function in humans?
(A) circulatory system (B) central nervous system (C) skeletal system (D) integumentary system

Ex Output:
B