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.

[EX Q]: The relationship between ticks and a dog can best be described as  
 (A) mutualism. (B) competition. (C) parasitism. (D) commensalism.
[EX A]: C

[EX Q]: 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.
[EX A]: C

[EX Q]: Which statement is true?  
 (A) All fungi are multicellular heterotrophs. (B) All fungi are single-celled heterotrophs. (C) All animals are multicellular heterotrophs. (D) All animals are single-celled heterotrophs.
[EX A]:
C