In this task, you are given a question and an answer, you would be asked to create the sentence based on the Question-Answer provided. It should be contained within the Question-Answer provided.
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Question: Question: Where are some of the greatest concentrations of species found? Answer: in the tropics

Answer: Some of the greatest concentrations of species are found in the tropics.


Question: Question: What is the term for matter that does not let any light pass through? Answer: opaque

Answer: Opaque is the term for matter that does not let any light pass through.


Question: Question: What is the name for a substance that can be used to follow the pathway of that substance through some structure? Answer: tracer

Answer:
A tracer is the name for a substance that can be used to follow the pathway of that substance through some structure.