At high temperatures enzyme activity declines
because of:

protein get denatured

Explanation:

at high temperatures enzyme activities in our body decline due To the proteins getting denatured

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.

the denominator has a very specific role.