Biology

The correct answer is: B.They consist of a single cell.

Here's why:

Unicellular means "one cell." When protists are described as unicellular, it means that each individual organism is composed of a single cell that carries out all the functions necessary for life, such as metabolism, growth, reproduction, and response to stimuli.

Why the other options are incorrect:

A."They are made up of multiple cells": This would describe multicellular organisms, not unicellular organisms. Protists, in this case, are not made of multiple cells.