6. Among the 27 points consisting of the 8 vertices, the midpoints of the 12 edges, the centers of the 6 faces, and the center of the cube, the number of groups of three collinear points is
(A) 57
(B) 49
(C) 43
(D) 37
(B)
6.【Analysis and Solution】The number of collinear triplets with both endpoints being vertices is $\frac{8 \times 7}{2}=28$; The number of collinear triplets with both endpoints being the centers of faces is $\frac{6 \times 1}{2}=3$; The number of collinear triplets with both endpoints being the midpoints of edges is $\frac{12 \times 3}{2}=18$, and there are no other types of collinear triplets. Therefore, the total number is $28+3+18=49$.