1. Set $A=\{a \mid a=12 m+8 n+4 l, m, n, l \in \mathbf{Z}\}, B=\{b \mid b=20 p+$ $16 q+12 r, p, q, r \in \mathbf{Z}\}, A, B$ the relationship between is ( ).
A. $A=B$
B. $A \nsubseteq B, B \nsubseteq A$
C. $A \supset B$
D. $A \subset B$
1. A.
$A=12 m+8 n+4 l=20 n+16 l+12(m-n-l) \in B$, so $A \subseteq B$.
Also, $b=20 p+16 q+12 r=12 r+8(2 q)+4(5 p) \in A$, so $B \subseteq A$, thus $A=B$.