下面的式子中，表示x与y互为倒数的算式是（  ）

①三楼地面到一楼地面的高度        ②从一楼到达三楼所用的时间

③每个同学的质量或体重            ④一楼到三楼楼梯的长度

A:____

B: Yes, please. I want a skirt for my daughter.

A: OK. How about this one?

B: Oh, it's small for me.

A:____

B: She's sixteen.

A: Oh, my daughter is 16, too. When is your daughter's birthday?

B:____

A: Great! Their birthdays are on the same day. What color does she like?

B: Blue.

A: Here is a blue skirt. Do you like it?

B:____I think my daughter likes it, too. How much is it?

A: 50yuan.

B:____.Thank you.

下列实验设计能达到实验目的的是(    )