You are presented with the quiz "Cells vary in size and shape and can only be seen with what?" 

But you don't know the answer, so you turn to your teacher to ask for hints. He says that "cells vary in size as well as shape, but all cells are very small" and "bacteria are single-cell microorganisms that are so small they can only be seen with a microscope". 

So, what's the best answer to the question?


 

 a microscope          