During Intercourse, Nathan Experiences Orgasm, but No Semen Appears

During intercourse, Nathan experiences orgasm, but no semen appears. His physician diagnoses his problem as retrograde ejaculation. This means that

A) muscles that normally close off the bladder fail to contract and semen enters the bladder.
B) no contractions have occurred in the muscles that surround the ejaculatory duct.
C) the erect penis has not sent a sufficient number of impulses to the ejaculatory center of the spinal cord.
D) the prostate and seminal vesicles fail to secrete their fluids, so no semen is created.