Jay Often Wakes Up with an Erection and Sometimes Experiences

Jay often wakes up with an erection and sometimes experiences erections throughout the night. What is the most likely reason for this?

A) Jay looks at porn before falling asleep which causes erotic dreams.
B) Jay's REM cycles occur throughout the night and right before he wakes up.
C) Jay drinks too much fluid before going to bed which causes pressure in his penis.
D) Jay does not masturbate frequently enough to release built-up amounts of semen.