Fact 1: Adult sponges are sessile.

Fact 2: Sessile Attached permanently, immobile.

Given the two facts above, answer the question "What are immobile?" with the following options: 
- sharks
 - sperm cells
 - an organism's body
 - adult sponges
 - critical organs
 - humans
 - gastropod shells
 - all matter


 

    adult sponges     