Which statement concerning the sphincters is correct?

A) The internal sphincter is under voluntary control.
B) The external sphincter is under voluntary control.
C) Both sphincters remain slightly relaxed at all times.
D) The internal sphincter surrounds the external sphincter.

The external sphincter not only surrounds the internal sphincter but also has a small section overriding the tip of the internal sphincter at the opening. The external sphincter is under voluntary control. Except for the passing of feces and gas, the sphincters keep the anal canal tightly closed.