Testosterone and estrogen are lipid-soluble signal molecules that cross the plasma membrane by simple diffusion. If these molecules can enter all cells, why do only specific cells respond to their presence?

• A. Nontarget cells possess enzymes that immediately degrade the molecules as they enter the cell.
• B. Nontarget cells lack the inactive enzymes that the signal molecules activate.
• C. The signal molecules diffuse from the cell before an effective concentration can be achieved.
• D. In nontarget cells, these signal molecules cross the membranes of the endoplasmic reticulum and are captured by vesicles.
• E. Nontarget cells lack the intracellular receptors that, when activated by the signal molecule, can interact with genes in the cell's nucleus.