How are valves in the circulatory system similar to sphincters in the digestive system?

a. both limit movement of substances through the system
b. both absorb excess fluid from the system
c. both add strength to the walls of the system
d. both actively push substances through the system
e. both control an exit to the system

Option A,

both limit movement of substances through the system

The sphincter muscle usually surrounds the openings in the body such as urethra, anus and performs the function of tightly closing the openings. When once the messages are received from the nervous system the sphincter relaxes and releases the material out of the opening during urination of excreting

The same is the function of valves in the circulatory system. They also prohibits the entry of blood from one chamber to other and then to the main circulatory system. The relaxes on receiving a signal from the brain and thus transfer blood from one chamber to the other.