Natural selection acts upon

a only recessive alleles
b alleles that are expressed
c only alleles that are the result of recent mutations
d only dominant alleles

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