When blood plasma filters out of capillaries to become interstitial fluid, most of the ________ are left behind in the capillaries.

A) plasma proteins
B) lipids
C) carbohydrates
D) nutrients
E) oxygen molecules

Plasma proteins are too large to pass through the walls of capillaries and remain in the bloodstream, while smaller molecules such as nutrients, oxygen, and carbon dioxide can pass through. Therefore, when blood plasma filters out of capillaries to become interstitial fluid, plasma proteins are left behind in the capillaries.