1 Let the universal set $U=\{x \mid 1 \leqslant x \leqslant 7, x \in \mathbf{N}\}, A=\{1,2,3\}$, if
$$
\complement_{U}(A \cap B)=\{1,2,4,5,6,7\},
$$

then the set $B$ could be ( ).
(A) $\{2,3,4\}$
(B) $\{3,4,5\}$
(C) $\{4,5,6\}$
(D) $\{5,6,7\}$
(1) Since $A \cap B=\{3\}$, choose B.