$17 \cdot 43$ 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)
［Solution］The problem can be represented by the following diagram. Clearly, there are two possible starting points $A$ and $B$ that satisfy the problem's requirements. Therefore, $x$ does not have a unique solution.
Hence, the answer is $(E)$.