6. (10 points) On the desktop, a regular hexagon paper piece with a side length of 1 is joined with a regular triangle paper piece with a side length of 1, requiring no overlap, and the joined edges must be completely coincident. Then the number of sides of the new shape formed is ( )
A. 8
B. 7
C. 6
D. 5
So, the number of sides of the combined shape is:
$$
6+3-4=5 \text { (sides) }
$$

Answer: The number of sides of the new shape obtained is 5. Therefore, the correct choice is: $D$.