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.

[Q]: 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
[A]: A


[Q]: When do mutations help make an ecosystem more sustainable?  
 (A) when mutations decrease the number of individuals in an ecosystem (B) when mutations increase the number of individuals in an ecosystem (C) when mutations decrease the number of species in an ecosystem (D) when mutations increase the number of species in an ecosystem
[A]: D


[Q]: Some wasp species lay their eggs inside living caterpillars. As the eggs mature, they use the caterpillar as a food resource. Eventually, the wasp larvae hatch out of the caterpillar. This type of relationship is best described as  
 (A) predator-prey. (B) parasitic. (C) mutualistic. (D) commensalistic.
[A]:
B