根据对话情景完成对话，使上下意思连贯。

A: Hello, 1.            Kate?

B: Sorry, she isn't in right now. Is that Susan speaking?

A: Yes. Who's that?

B: This is Mike. 2.           ?

A: Fine, thanks. Can I leave a message?

B: Of course. 3.            please. I'll go and get a pen. ( Soon Mike returns.) OK, please.

A: I'd like to ask her if she'll go to the English Festival next week. Will you please tell her to call me 

    back when she returns?

B: No problem. 4.           ?

A: It's 78340631.

B: OK, bye-bye.

A: Thanks. 5.             

让一凸透镜正对太阳，拿一张白纸在它的另一侧来回移动，直到白纸上的光斑变得最小最亮，这个最小最亮的点叫凸透镜的_____．若这一点到透镜光心的距离为15cm，如果用这样的凸透镜做照相机镜头，物体离镜头的距离至少应大于______cm．