16.18 Point $A$ and $B$ are 5 units apart, on a given plane passing through points $A$ and $B$, how many lines are 2 units away from point $A$ and 3 units away from point $B$
(A) 0.
(B) 1.
(C) 2.
(D) 3.
(E) More than 3.
(41st American High School Mathematics Examination, 1990)
[Solution] As shown in the figure, there are 3 lines that satisfy the problem's conditions. Note the line $l_{1}$ perpendicular to $A B$. Therefore, the answer is $(D)$.