2. If the non-empty set $A=\{x \mid 2 a+1 \leqslant x \leqslant 3 a-5\}, B=\{x \mid 3 \leqslant x \leqslant 22\}$, then the set of all $a$ that makes $A \subseteq A \cap B$ true is
(A) $\{a \mid 1 \leqslant a \leqslant 9\}$
(B) $\{a \mid 6 \leqslant a \leqslant 9\}$
(C) $\{a \mid a \leqslant 9\}$
(D) $\Phi$
(B)
2.【Analysis and Solution】From the problem, we have $A \subseteq B$.
$$
\therefore\left\{\begin{array}{l}
2 a+1 \geqslant 3, \\
3 a-5 \leqslant 22, \\
3 a-5 \geqslant 2 a+1 .
\end{array}\right.
$$

Solving, we get $6 \leqslant a \leqslant 9$.