An unusual tower is built with cubes starting with one in the bottom layer, then 4 in the second layer, 9 in the third, then 16, and so on.

Altogether 91 cubes are used to build the tower.

How many layers does the tower have?

 

A. \( 7\)B. \( 6\)C. \( 5\)D. \( 4\)E. \( 3\)