During male ejaculation, the internal urethral sphincter closes tightly to _______?
1) prevent urine from leaking into the urethra
2) isolate the ureters from the urinary bladder
3) block movement of mucus from the bulbourethral gland into the ejaculatory duct
4) keep sperm from moving into the ductus deferens
5) allow seminal vesicle to transfer sperm to the epididymis
