Im board in this stupid class

The cretaceous period spanned the time interval between and 65 million years ago. 250 million 144 million 75 million 200 million

Which of these would most likely be a stimulus that would cause the body to initiate feedback mechanisms a.) normal body temperature in an arctic environment b.) normal boy temperature in a tropical environment c.)light physical activity d.)low blood sugar

What characteristic makes a cell membrane selectively permeable