Given the task definition, example input & output, solve the new input case.
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.
Example: Which event can cause a large rock to become soil over time? 
 (A) decaying (B) an earthquake (C) a landslide (D) weathering
Output: D
Under the action of heat, cold, rain, wind, and other atmospheric factors, the rock breaks down physically into small fragments that become the parent material of the soil. Also, atmospheric factors change according to weather.

New input case for you: A sample in a cylindrical container has a cylindrical shape and a fixed volume. The state of matter of the sample   
 (A) must be solid. (B) could be either solid or liquid. (C) must be liquid. (D) could be either liquid or gas.
Output:
B