After Visiting His Doctor for Erectile Dysfunction, a Man Is

After visiting his doctor for erectile dysfunction, a man is prescribed sildenafil, a drug that prevents cGMP from being degraded.This drug is most likely to help this man's condition by

A) relaxing smooth muscle cells associated with penile arteries.
B) inhibiting the release of the gaseous neurotransmitter, nitric oxide.
C) causing penile smooth muscle cells to release nitric oxide.
D) constricting penile arteries, causing the penis to become hard and erect.
E) triggering penile nerves to release increased amounts of cGMP.