$17 \cdot 43$ A person walks $x$ miles due west, then turns $150^{\circ}$ to the left and proceeds 3 miles in the new direction. As a result, he is $\sqrt{3}$ miles from the starting point. Then $x$ is
(A) $\sqrt{3}$.
(B) $2 \sqrt{3}$.
(C) $\frac{3}{2}$.
(D) 3.
(E) There is no unique solution according to the given conditions.
(31st American High School Mathematics Examination, 1980)