4. (8 points) As shown in the figure, the area of the regular octagon $A B C D E F G H$ is 1, and there are two squares $A C E G$ and $P Q R S$. What is the area of the shaded part in the regular octagon?
A. $\frac{1}{2}$
B. $\frac{2}{3}$
C. $\frac{3}{5}$
D. $\frac{5}{8}$
【Answer】Solution: According to the analysis, the shaded area in the figure is transformed into an equivalent area. It is not difficult to see from the figure that the shaded area and the blank area are exactly equal. The shaded area in the regular octagon accounts for: $\frac{1}{2}$, so the correct choice is: $A$.