A rectangular yard contains two flower beds in the shape of congruent isosceles right triangles. The remainder of the yard has a trapezoidal shape, as shown. The parallel sides of the trapezoid have lengths 15 and 25 meters. What fraction of the yard is occupied by the flower beds?

**Answer Choices**

A. \dfrac{1}{8}

B. \dfrac{1}{6}

C. \dfrac{1}{5}

D. \dfrac{1}{4}

E. \dfrac{1}{3}