Fact 1: Ejaculation occurs when muscle contractions propel sperm from the epididymes.

Fact 2: Ejaculation is the expulsion of semen.

Given the two facts above, answer the question "The expulsion of semen occurs when what propels sperm from the epididymes?" with the following options: 
- birth
 - muscle contractions
 - kinetic energy
 - urine
 - rapid expansion
 - air
 - heat produced
 - matter vibrating


 

  muscle contractions       