$19 \cdot 48$ polygon $A B C D E F G H$ has adjacent sides that are perpendicular to each other. To find its perimeter, the minimum number of side lengths required is
(A) 3 .
(B) 4 .
(C) 5 .
(D) 6 .
(2nd "Jinyun Cup" Junior High School Mathematics Invitational, 1985)
[Sol] First, we can see that $A H+G F+E D=B C$, so for the horizontal sides, we only need to know the length of $B C$.

For the vertical sides: $H G+D C=A B+E F$, so we only need to know the lengths of $A B$ and $E F$ to find the length of $A B+H G+E F+D C$.
In summary, we only need to know the lengths of 3 sides.
Therefore, the answer is $(A)$.