TASK DEFINITION: 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.
PROBLEM: One of the main causes of acid rain is
(A) Waste from nuclear power plants (B) Spills from chemical manufacturing plants (C) Gases from burning fossil fuels (D) Gases from aerosol spray cans

SOLUTION: C

PROBLEM: 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.

SOLUTION: C

PROBLEM: In one day, a family in a car rode for 2 hours, stopped for 3 hours, and then rode for another 5 hours. During the day, the family traveled a total distance of 400 kilometers. What was their average speed for the whole trip?
(A) 10 km/h (B) 20 km/h (C) 40 km/h (D) 50 km/h

SOLUTION:
C