Question

William is observing a single-celled organism under a microscope and notices that it has a nucleus and is covered in small, hair-like structures.

Answer 1

The name of this organism is PROTIST.
This is because, protists are single celled organisms that have true nucleus and they are typically covered with tiny, hair-like structure that are called cillia. The cillia normally moves forward and backward very quickly, thus propelling the organism through water.