An environmental change causes the

contractile vacuoles of a paramecium to stop

functioning, while most of the other cell

structures appear to be unaffected. Which

environmental change would most likely

produce this result?

The correct option is slight increase in salt concentration in the

environment.

Explanation:

The main function of contractile vacuole in the body of a paramecium is to pump out excess water. But an increase in salt concentration in the environment will let the water move inside the cell by osmosis. Hence, the contractile vacuole will not perform its function and will not be able to regulate osmoregulation.

Other options are incorrect because slight changes in the temperature or pH won't affect the contractile vacuole and it will still be able to perform its function.