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.

Question: Which of the following has changed over the last 200 years primarily due to human activity? Answer: the composition of the atmosphere
The composition of the atmosphere has changed over the last 200 years primarily due to human activity.

Question: What type of substance is any matter that has a fixed chemical composition and characteristic properties? Answer: pure chemical substance
Pure chemical substance type of substance is any matter that has a fixed chemical composition and characteristic properties.

Question: What type of creature is noted for having its eyes at the tips of stalks or tentacles that emerge from its head? Answer: gastropods

A(n) gastropods is noted for having its eyes at the tips of stalks or tentacles that emerge from its head.