Which statement best explains homeostasis?

a process by which organisms keep internal conditions relatively constant despite changes in external conditions

a process by which organisms maintain a low level of energy use when faced with changes in external conditions

a process by which organisms seek a stable external environment when they can't change their internal conditions

The homeostasis is an organism's ability to maintain a stable internal environment. It is a mechanism that controls internal conditions of an organism so that internal conditions remain stable without regard to the external conditions. So, it regulates body temperature, water level, sugar level, etc. For example, if body temperature is increased, the body detects the change and activate mechanisms that decrease body temperature. 

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.

did you fail the test? xd