A cube with side length 1 is sliced by a plane that passes through two diagonally opposite vertices A and C and the midpoints B and D of two opposite edges not containing A or C, as shown. What is the area of quadrilateral A B C D ?

**Answer Choices**

A. \dfrac{\sqrt{6}}{2}

B. \dfrac{5}{4}

C. \sqrt{2}

D. \dfrac{3}{2}

E. \sqrt{3}