GAUSS8 2008 Problem 16

A 4\times4 square grid can be entirely covered by three non-overlapping pieces made from 1\times1 squares. If the first two pieces aregauss8 2008 16 and gauss8 2008 16b, the third piece is

Answer Choices
A. gauss8 2008 16a
B. gauss8 2008 16b
C. gauss8 2008 16c
D. gauss8 2008 16d
E. gauss8 2008 16e