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.

Example input: Which part of a bicycle BEST moves in a circle?
(A) Seat (B) Frame (C) Foot pedal (D) Kickstand
Example output: C
Example explanation: Seat, frame and Kickstand are static parts of the bicycle, even when bicycle moves. Foot pedal moves in a circle as bicycle moves.
Q: Use the information below to answer the question. In solid fuel rockets, a fuel mixture is burned and once the mixture starts burning it cannot be stopped. In liquid fuel rockets, there is a tank of fuel and a tank of oxygen. The burning of the fuel can be stopped by preventing the flow of fuel and oxygen into the combustion chamber. Based on this information, which system is more highly developed in liquid fuel rockets than in solid fuel rockets?
(A) propulsion (B) suspension (C) control (D) structure
A:
C