20. The figure below is a large rectangular prism formed by three smaller rectangular prisms. Now, we need to color it using three colors. The requirements are:
(1) Two adjacent faces of each smaller rectangular prism must be colored with different colors (by "adjacent" we mean these two faces share a common edge).
(2) If two smaller rectangular prisms have two faces that overlap, then these overlapping faces must be colored the same color; according to the above requirements, there are (
) different ways to color it.
12
【Answer】If the large rectangular prism is not counted as a rectangular prism, then the left rectangular prism has 6 coloring methods: the colors of opposite faces must be the same, so it is $3 \times 2 \times 1=6$; once the side colors are determined, the side colors of the two smaller rectangular prisms on the right are also determined; there are 2 remaining, so there are a total of 12 different coloring methods;
However, if the large rectangular prism is also counted as a rectangular prism, then directly coloring the large rectangular prism, the answer is 6;

Personally, I believe the large rectangular prism should not be counted as a rectangular prism, otherwise, directly coloring the large one would lose the meaning of the test......so I tend to the answer being 12