3. Among the 8 vertices, the midpoints of the 12 edges, the centers of the 6 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
3. $\mathrm{B}$ 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 centers of edges is $\frac{12 \times 3}{2}=18$; and there are no other types of collinear triplets. Therefore, the total number is $28+3+18=49$.