Antiandrogens treat benign prostatic hypertrophy by b) blocking alpha-1 receptors found in smooth muscle in the bladder neck and prostrate, causing them to relax c) stimulating parasympathetic nerves to bring about contraction of the urinary bladder d) blocking parasympathetic nerve impulses to reduce the strength and frequency of contractions of the urinary bladder.

Option B, blocking alpha-1 receptors found in smooth muscle in the bladder neck and prostrate, causing them to relax

Explanation:

The subtype alpha (1A) of alpha (1) adrenoceptors are mainly responsible for expressing and contracting bladder neck, urethra and prostate thereby enhancing bladder outlet particularly in elder men (45 Years above) who have enlarged prostates.  

If this alpha-1 andrenoceptors found in smooth muscle of bladder neck and prostrate are blocked somehow, then the muscles will relax  and this how antiandrogens are used for treat ing benign prostatic hypertrophy  

If these α1A subtype receptors are stimulated by norepinephrine, then smooth muscles are caused thereby producing a physical block at the bladder neck

Hence, option B is correct