In the diagram, 3 of the 1 \times 1 squares that make up the 4 \times 5 grid are shaded. How many additional 1 \times 1 squares need to be shaded so that one-half of all of the 1 \times 1 squares are shaded?
Answer Choices
A. 5
B. 9
C. 7
D. 6
E. 8