Question

___________ is a structure that contains spores and is located on the underside of fern leaves.
Basidium
Bacillus
Cilium
Sorus

Answer 1

The answer is "Sorus"
So it is D because 
Sorus is a structure that contains spores and is located on the underside of fern leaves.

Answer 2

Answer:

located on the lower surface of fern leaves. they’re essential for reproduction