6. As shown in Figure 2, modules (1)-(5) are each composed of 4 small cubes with an edge length of 1, and module (6) is composed of 15 small cubes with an edge length of 1. Now, three modules are selected from modules (1)-(5) to be placed on module (6) to form a large cube with an edge length of 3. The number of ways to select three modules from modules (1)-(5) to complete the task is ( ).
(A) 1
(B) 3
(C) 5
(D) 10
6. B.

From modules (1)-(5) in Figure 2, selecting three modules to complete the task is not unique.

In fact, from the position of the gap in module (6), one can first choose module (5) and embed it in the gap of module (6), at which point the accumulated shape is as shown in Figure 8. Next, select two modules from modules (1)-(4) and connect them to form the shape shown in Figure 9. This can clearly be achieved by connecting modules (1) and (2) or (1) and (4) (as shown in Figure 10).

Therefore, selecting modules (1), (2), (5) or (1), (4), (5) can complete the task. However, choosing modules (2), (3), (4) can also complete the task (as shown in Figure 11).