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]: What type of force keeps the planets orbiting the Sun?  
 (A) gravitational (B) magnetic (C) electrical (D) nuclear
[EX A]: A

[EX Q]: Sofia put a bat house in a tree in her yard. The bats ate mosquitos in Sofia's yard at night and roosted in the house during the day. Droppings from the bat house nourished the tree. What kind of relationship exists between Sofia, the bats, and the tree?  
 (A) The relationship is competitive. (B) The relationship is cooperative. (C) The relationship is parasitic. (D) The relationship is predatory.
[EX A]:
B