Sperm must undergo , which is a physiologic conditioning, before they can accomplish . This conditioning occurs in the reproductive tract, and typically lasts several .

The speed of  sound:   sound travels  at different speeds depending on what it istraveling through. of the three mediums (gas, liquid, and solid)  sound waves travel the slowest through  gases, faster  through  liquids, and fastest  through  solids.

Ibelieve z is the second because it looks like tissues, where has y is first because it's a cell, and the others look like organs or body parts.