Research on the changing reproductive systems of adult men has found that:

A. testosterone levels of young men are relatively stable across the day, while levels for men over 40 are higher in the morning and lower in the evening

B. testosterone levels are higher in the fall and lower in the spring for all men

C. men over 60 have a testicular volume that is one-half the volume of a young adult male

D. benign prostatic hyperplasia is a very common change for older adult men