Oxygen and Carbon Dioxide Are Able to Pass Through the Plasma

Oxygen and carbon dioxide are able to pass through the plasma membrane of a cell because

A) they are both polar molecules.
B) both are lipid soluble.
C) they move through ion pores.
D) each binds to a transport protein that "pulls" it across the membrane.
E) they are small and nonpolar and readily pass between phospholipids.