Which of the following is a correct statement about an organism and its environment?
a. the gastrovascular cavity provides the nutrient exchange surface in mammals.
b. an animal is a closed system that is separate and distinct from its environment.
c. interstitial fluid is the go-between for body cells and the circulatory system.
d. animals are able to live as long as they remain isolated from their environments. e. none of the choices is correct.

correct answer is option a.

tropopause, stratopause and mesopause have all in common aspect that is point of maximum temperature in its layer of the atmosphere. all layers of atmosphere observe abrupt change in temperature. tropopause is the boundary between troposphere and stratosphere. stratopause is the boundary between stratosphere and mesosphere. mesopause is the boundary between mesosphere and thermosphere. these all boundaries are ranges between altitude of 0 to 80 km.