You are presented with the quiz "Viruses are so small that to see them a scientist would have to use what kind of lens?" 

But you don't know the answer, so you turn to your teacher to ask for hints. He says that "viruses are so small that they can be seen only with an electron microscope" and "on the surface of each microscopic color filter is also a microscopic lens". 

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


 

   an electron lens        