instruction:
You are given a science question (hard-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.
question:
Some bacteria use iron found in their systems as a means to guide their movement. Which stimulus most likely triggers this movement mechanism?  
 (A) magnetism (B) oxygen (C) light (D) heat
answer:
A


question:
Which action creates competition between environmental concerns and economic gains?  
 (A) protecting endangered wildlife (B) reintroducing wildlife into their natural habitats (C) using forest land to build homes (D) using city buses for transportation
answer:
C


question:
Which characteristic do single-celled organisms and multicellular organisms have in common?  
 (A) Both have cells with specialized functions for each life process. (B) Both perform all life processes within one cell. (C) Both have a way to get rid of waste materials. (D) Both are able to make food from sunlight.
answer:

C