You will be given a definition of a task first, then an example. Follow the example to solve a new instance of the task.
You are given a science question (easy-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 part of a bicycle BEST moves in a circle? 
 (A) Seat (B) Frame (C) Foot pedal (D) Kickstand
Solution: C
Why? Seat, frame and Kickstand are static parts of the bicycle, even when bicycle moves. Foot pedal moves in a circle as bicycle moves.

New input: Which of these best demonstrates the characteristics of science?  
 (A) One student lifts a rock and skips it across a stream. (B) One student thinks about rocks and writes down his opinion. (C) Two students study a rock and then compare their observations. (D) Two students remove rocks from a garden and then plant flowers.
Solution:
C