Which Statement About Precapillary Sphincters Is CORRECT

Multiple Choice

Which statement about precapillary sphincters is CORRECT?

A) They contract when oxygen levels in the tissue are low.
B) They can close off the capillaries by contracting.
C) They are openings that allow large molecules and blood cells to leave the capillary.
D) When the precapillary sphincters are open, blood flows only through the thoroughfare channels.
E) They are voluntary.