Osteoporosis is a disease in which removes some of the material in the bones. This weakens the bones so that they break easily. Doctors often advise people with osteoporosis to exercise regularly. What is the most likely reason for this advice?

The current thought on the structure of the cell membrane is: a. a static phosphate sandwich of lipids b. a fluid-mosaic of phospholipids and proteins c. a bilayer of proteins with static lipid molecules d. an impermeable bilayer of protein molecules e. a static and permeable phospholipid single layer