A: Good morning, Tina. Long time no see!____ ?

B: Yeah, I went to Beijing last month.

A: Great! And are you free now?

B: Yes.____?

A: I am going to make some plans about the summer vacation. Can you give me some advice?

B:____  How about going to volunteer in the Old People's Home?

A:____Can you join with me?    

B: OK! I think we will have a good time. Oh, I have to finish my homework now. See you later!

A:____

科学家在研究化学物质吋，常常对物质逬行分类，以便对同类物质的组成和性质进行深人的研究，下列4组物质：

①Ca、S、Cl₂、NO₂②NH₃•H₂O、Na₂CO₃、CH₄、KCl③H₂CO₃、H₂SO₄、NaOH、H₂SiO₃④MgO、SO₂、CO₂、SiO₂从物质的基本分类看，每组中都有一种物质与其它物质不属于同这4种物质分别是（    ）