Fact 1: Cells vary in size as well as shape, but all cells are very small.

Fact 2: Most cells are too small to be seen without a microscope.

Given the two facts above, answer the question "What vary in size as well as shape and cannot be seen without a microscope?" with the following options: 
- bushes
 - matter
 - cells
 - grains
 - sand
 - bones
 - apples
 - small


 

   cells      