6. (10 points) In the figure, the side length of the square is 10, then the area of the shaded part is ( )
A. 56
B. 44
C. 32
D. 78
【Analysis】As shown in the figure below, the figure is cut in such a way that the sum of the areas of the blank parts $a, b, c, d$ is equal to the area of the corresponding shaded parts. Finding this equal relationship will solve the problem.
【Solution】Solution:
As shown in the figure, it can be seen that: the sum of the areas of the blank parts $a, b, c, d$ is equal to the area of the corresponding shaded parts; $\square$

The area of the blank parts $=$ (Area of the square $-3 \times 4$ of the small rectangles) $\div 2=(10 \times 10-3 \times 4) \div 2=44$;
The area of the shaded parts $=$ Area of the square - Area of the blank parts $=10 \times 10-44=56$.
Therefore, the answer is: $A$.