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]: In an experiment studying phototropism, students grew bean plants in labeled cardboard milk cartons. Afterward, the plants and soil were properly discarded. Which instruction line BEST conserves the remaining resources?  
 (A) recycle the markers, reuse the milk cartons (B) reuse the markers, discard the milk cartons (C) discard the markers, reuse the milk cartons (D) reuse the markers, recycle the milk cartons
[A]: D


[Q]: Why would animals most likely have to leave an area during a drought?  
 (A) to find mates (B) to find shelter (C) to escape predators (D) to find water and food
[A]: D


[Q]: In which process is nitrogen from the air put into a form that plants can use?  
 (A) nitrification (B) denitrification (C) nitrogen saturation (D) nitrogen fixation
[A]:
D