根据对话内容，补全对话

A: What can I do for you?

B：I want to buy a pair of shoes.

A:____

B: Size eight or nine.

A: Ok! How about this pair?

B: Sorry, I do not like black.____

A: Yes. We have blue, white and brown ones .

B: Can I havea look at the brown ones?

A: Yes, please.

B: ____

A: Forty-sixyuan.        

B: It is too expensive. ____

A: How about forty?    

B: It is still expensive. What about thirty-five?

A: All right.

B: OK.____

Where are the two speaking?

气体的压强是由于组成气体的____向各个方向运动，撞击器壁而产生的；对此，我们可以通过小钢球自由落下不断撞击托盘后弹出，并使磅秤上有一持续示数的实验（如图）来进行____（选填“观察”“类比”“分析”或“综合”）．