2. Among all the subsets of the set $M=\{1,2, \cdots, 10\}$, there is a family of distinct subsets such that the intersection of any two of them is not empty. Then, the maximum number of subsets in this family is ( ) .
(A) $2^{10}$
(B) $2^{9}$
(C) $10^{2}$
(D) $9^{2}$
(提示: 对 $M$ 的任一子集 $A$, 易知 $A$ 与 $M-A$ 至多有一个在题设的子集族, 力中, 故 $\mid$. $b \mid \leqslant 2^{9}$.)

( Hint: For any subset $A$ of $M$, it is easy to see that at most one of $A$ and $M-A$ is in the given family of subsets, so $\mid$. $b \mid \leqslant 2^{9}$. )