Why do plants have rigid barks

Bark is the outermost covering of a tree's trunk and branches, like a protective skin. Tree bark conserves water and also serves to protect the tree's essential living systems from environmental and situational dangers. These include temperature extremes, storms, attacks by animals, diseases, and insects.

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.