Cilia:

A. are microtubule-based structures.
B. are short projections.
C. help the cell move through its environment.
D. when they are present, occur in large numbers on a single cell.
E. All of the answer options are correct.

E. All the answer options are correct.

Explanation:

Cilia are very small hair-like, membrane-bound cell structures. They are present on the surface of many eukaryotic cells. They are made of microtubules and are continuous with the plasma membrane of a cell. On a single cell, they are present in large numbers as compared to flagella. The major function of cilia is to move the cell or to move substances such as mucous, fluid over or around the cell.