3. The face of a clock is circular, with 12 equally spaced points on its circumference to indicate the hours. The number of rectangles that can be formed using these points as vertices is ( ).
(A) 6
(B) 12
(C) 15
(D) 24
3.C.

In the lines connecting the equal division points, there are 6 diameters. Each pair of diameters forms the diagonals of 1 rectangle, resulting in $\frac{6 \times 5}{2}=15$ pairs, hence yielding 15 rectangles.