1. Let the set
$$
M=\{x \mid 0<x \leqslant 3\}, N=\{0<x \leqslant 2\} \text {. }
$$

Then “ $a \in M$ ” is “ $a \in N$ ” ( ).
(A) a sufficient but not necessary condition
(B) a necessary but not sufficient condition
(C) a necessary and sufficient condition
(D) neither a sufficient nor a necessary condition
1. B.

Since $N \subseteq M$, " $a \in M$ " is a necessary but not sufficient condition for " $a \in N$ ".