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.

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.
C

Which object is best used to demonstrate the bending of light as it passes through a substance?  
 (A) convex lens (B) flat mirror (C) opaque rod (D) concave mirror
A

In the Northern Hemisphere, June 21st has more hours of sunlight than any other day. However, June 21st has the fewest hours of sunlight in the Southern Hemisphere. Which best explains why the Northern Hemisphere receives more daylight than the Southern Hemisphere on the same day?  
 (A) Earth rotates on its axis (B) Earth is tilted on its axis (C) The Sun moves closer to the Northern Hemisphere (D) The Sun releases more energy to the Northern Hemisphere

B