Which of the following best describe a crevasse? a crack in the topmost section of a glacier a piece of a glacier that breaks off and floats in water a lowland region formally filled with water an ice mass that flows through an area originally occupied by a stream

A crack in the topmost section of a glacier.

Crevasse is a deep crack on the top most ice of a glacier. Crevasse forms where the ice is brittle. It is also known as glacial fracture. This results due to stress developed in the glacier ice. Crevasse usually form in the upper layer of the glacier where the ice is more brittle than deeper ice. Deeper ice does not break and fracture as the glacier moves.

the correct answer is:

a population changes in response to a change in the environment.