6. Among the 8 vertices, 12 midpoints of edges, 6 centers of faces, and the center of the cube, a total of 27 points, the number of groups of three collinear points is ( ).
(A) 57
(B) 49
(C) 43
(D) 37
6. B.

The number of collinear triplets with both endpoints being vertices is $\frac{8 \times 7}{2}=28$ (groups); the number of collinear triplets with both endpoints being the centers of faces is $\frac{6 \times 1}{2}$ $=3$ (groups); the number of collinear triplets with both endpoints being the midpoints of edges is $\frac{12 \times 3}{2}=18$ (groups), and there are no other types of collinear triplets. Therefore, the total number is $28+3+18=49$.