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.
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Question: When manned space exploration began, NASA used the gravity assist concept so that spacecraft could conserve fuel. Which statement explains why the gravity assist concept was useful for spacecraft to successfully travel and return to Earth?  
 (A) It gave spacecraft a timed trajectory. (B) It ensured spacecraft would return home safely. (C) It was helpful in planning spacecraft trajectories. (D) It ensured spacecraft would avoid being pulled into the sun.

Answer: C


Question: Which action involving a pulley system requires the least amount of force?  
 (A) using several pulleys together instead of a single pulley (B) using a fixed pulley instead of a moveable pulley (C) pulling a long rope instead of a short rope (D) pulling a rope up instead of down

Answer: A


Question: Which procedure correctly describes materials combining?  
 (A) Salt and sand are added to hot water and stirred making a mixture. (B) Oil and water are placed in a sealed bottle and shaken making a compound. (C) Sugar and water are added to flour and cooked in an oven making an element. (D) Soil and water are shaken in a container and left to separate forming two elements.

Answer:
A