在下列固体中分别加入NaOH浓溶液，固体溶解但无气体生成的是（　　）

A．SiO₂

B．Na

C．Al

D．NH₄Cl

--- Excuse me, can I have a talk with Mr. Miller this afternoon?

---A moment, please. Let me check_______.

A．if Mr. Miller will be free

B．when will Mr. Miller have time

C．if Mr. Miller had a meeting

D．when does Mr. Miller come back