下列对组成细胞分子的描述，正确的是（　　）

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:____

约翰和大卫曾在发生核泄漏事故的电厂附近生活过。最近发现约翰的儿子患有常染色体的隐性遗传病甲，大卫的女儿患有常染色他显性遗传病乙，约翰与大卫及他们的妻子都很正常。请根据上述材料来回答问题：