You are presented with the question "The expulsion of semen occurs when what propels sperm from the epididymes?" and the following answer choices: 
- birth
 - muscle contractions
 - kinetic energy
 - urine
 - rapid expansion
 - air
 - heat produced
 - matter vibrating

Now knowing that ejaculation occurs when muscle contractions propel sperm from the epididymes and ejaculation is the expulsion of semen, choose the best answer.


 

  muscle contractions       