Let S be the set of all points (x, y) in the coordinate plane such that 0 \leq x \leq \dfrac{\pi}{2} and 0 \leq y \leq \dfrac{\pi}{2}. What is the area of the subset of S for which
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\sin ^{2} x-\sin x \sin y+\sin ^{2} y \leq \dfrac{3}{4} ?
Answer Choices
A. \dfrac{\pi^{2}}{9}
B. \dfrac{\pi^{2}}{8}
C. \dfrac{\pi^{2}}{6}
D. \dfrac{3 \pi^{2}}{16}
E. \dfrac{2 \pi^{2}}{9}