4. As shown in the figure, the lower base of the isosceles trapezoid is twice the upper base. If the distances from a point inside the trapezoid to the four sides of the trapezoid are such that the distance to the upper or lower base is the smallest, then this point is called a "Hope Point". If a point is randomly taken inside the trapezoid, the probability that this point is a "Hope Point" is $\qquad$ .
A. $\frac{1}{4}$
B. $\frac{1}{3}$
C. $\frac{2}{3}$
D. $\frac{1}{2}$
E. $\frac{3}{5}$
$\mathrm{C}$