You are presented with the quiz "What vary in size as well as shape and cannot be seen without a microscope?" 

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 "most cells are too small to be seen without a microscope". 

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


 

   cells        