2. 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
(提示: 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 $\frac{12 \times 3}{2}=18$. Therefore, there are $28+3+18=49$ in total.)