What strengthens and to maintain the fluid nature of a cell regardless of temperature?

Cholesterol in Cell membrane  strengthens and helps to maintain the fluid nature of a cell regardless of temperature

Explanation:

All organisms are made up of one or more cells. Each cell is protected or differentiated by a covering called as the cell membrane. Phospholipids are the basic structure of the cell membrane. Cholesterol prevents the loss of fluid from phospholipids.  

Cell membrane has a lipid layer and cholesterol which is placed between the phospholipids to maintain the fluid nature of the cell under different temperature. Cholesterol prevents the cell from solidifying and helps maintain the fluid. Cholesterol actually acts as a buffer between different temperatures.

the answer would be d

i'd say that the moon rock is about 2.2 billion years old.