Why are ostia important to sponges? a) They are the pores through which water, sperm, and food enter the sponge.
b) are large openings in the sponge that allow the waste to exit.
c) They are what the gel is composed of that connects all the different cells of the sponge together.
d) They pull water into the sponge through the beating of their flagella.

I'm so confused! If someone could help, it would mean a lot. Thank you and PLEASE no links!