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]: Your community is planning to build a new sanitary landfill. In locating the landfill, which is the most important environmental consideration?  
 (A) the cost of the land (B) the location of the groundwater (C) the proximity to an industrial park (D) the accessibility to a major highway
[EX A]: B

[EX Q]: Lichens are symbiotic organisms made of green algae and fungi. What do the green algae supply to the fungi in this symbiotic relationship?  
 (A) carbon dioxide (B) food (C) protection (D) water
[EX A]: B

[EX Q]: Which is an example of a chemical change?  
 (A) sand separated from water by filtering (B) water evaporating from a puddle (C) a rock being eroded by wind (D) a nail rusting in water
[EX A]:
D