3. There is a kind of football made by sewing together several pieces of black and white cowhide, with black pieces being regular pentagons and white pieces being regular hexagons (as shown in Figure 1). If a well-sewn football of this type has 12 black pieces, then the number of white pieces is ( ).
(A) 16
(B) 18
(C) 20
(D) 22
3.C.

From the problem, we know that each white patch is adjacent to 3 black patches and 3 white patches, while each black patch is only adjacent to 5 white patches. Therefore, the number of white patches is
$$
\frac{12 \times 5}{3}=20 \text { pieces. }
$$