Which of the Following Is the Correct Sequence in the Process

Which of the following is the correct sequence in the process of a man's erection?

A) Nerve impulses from the sympathetic nervous system cause the release of norepinephrine, which causes the contraction of smooth muscle.
B) The release of nitric oxide causes blood flow into the sinusoids, closing off veins from the sinusoids.
C) Increased activity of sympathetic fibers causes an increase in the activity of parasympathetic fibers.
D) Ongoing contraction of the smooth muscle of the arterioles causes restriction of blood flow into the sinusoids.
E) None of the above