6. A cube with an edge length of 5 is sawed into 125 smaller cubes with an edge length of 1. Then, at least ( ) cuts are needed.
(A) 7 times
(B) 8 times
(C) 9 times
(D) 12 times
6. (C).

Each time you saw, you can rearrange the pieces that have been sawed. To minimize the number of sawing times, you only need to consider how many more times the largest piece needs to be sawed. First, saw the $5 \times 5 \times 5$ cube once, and the largest piece will be at least $5 \times 5 \times 3$; after sawing twice, the largest piece can be $5 \times 3 \times 3$ or $5 \times 5 \times 2$. Let's consider the case of $5 \times 3 \times 3$ (the case of $5 \times 5 \times 2$ can be considered similarly), after sawing three times, you get a large piece of $3 \times 3 \times 3$, and the center of this piece has a unit cube whose six faces all need to be sawed. Therefore, you need to saw at least 6 more times, so the total number of sawing times is at least 9.