19. (5 points) There are 4 pieces of part $A$ each weighing 5 tons, 6 pieces of part $B$ each weighing 4 tons, 11 pieces of part $C$ each weighing 3 tons, and 7 pieces of part $D$ each weighing 1 ton. If all the parts need to be transported in one go, at least how many trucks with a capacity of 6 tons are required? $\qquad$
【Answer】Solution: Let (1) represent a part weighing 1 ton, (3) represent a part weighing 3 tons, (4) represent a part weighing 4 tons, and (5) represent a part weighing 5 tons. The specific combinations are as follows:
$$
\begin{array}{l}
\text { (5)+(1); (5)+(1); (5)+(1); (5)+(1); (3)+(3); (3)+(3); (3)+(3); (3)+(3); (3)+(3); (4)+(1); } \\
\text { (4)+(1); (4)+(1); (3); (4); (4); (4); }
\end{array}
$$

A total of 16 trucks.