17. (6 points) $A, B, C, D$ are four points arranged from left to right on a straight line. Using these four points as endpoints, six line segments can be formed. It is known that the lengths of these six line segments are $12, 18, 30, 32, 44, 62$ (unit: centimeters). Therefore, the length of line segment $BC$ is $\qquad$ centimeters.
【Analysis】As shown in the figure, according to the problem, $A D=62 \mathrm{~cm}, A B+B C+C D=62=12+18+32$; also, because $30=12+18,44=12+32$, so $B C=12 \mathrm{~cm}$.

【Solution】According to the problem, we can get: $A D=62 \mathrm{~cm}, A B+B C+C D=62=12+18+32$;
also, because $30=12+18,44=12+32$,
so $B C=12 \mathrm{~cm}$.
Answer: The length of line segment $B C$ is 12 centimeters.
Therefore, the answer is: 12.
【Comment】This problem examines length comparison. Note that in the given figure, line segment $B C$ is the shortest line segment on the straight line.