根据对话理解，选择最佳答案填空。

A: 1 I help you?

B: Yes, please! I 2 a T-­shirt.

A: A T-­shirt? What 3 do you want?

B: Red.

A: Have a look 4 this one! It's on sale.

B: Oh, it's really nice, 5 it is too short, can you give me a 6 one?

A: Ok! How about this red one?

B: En……, it's great! I like it! How much 7 it?

A: 25 dollars 8.

B: That's good. I'll 9 it.

A: Here you are!

B: Thank you 10!

每两人比赛1场，一共要赛____场．

如图；现有一迷失方向的小青蛙在3处，它每跳动一次可以等机会地进入相邻的任意一格（如若它在5处，跳动一次，只能进入3处，若在3处，则跳动一次可以等机会进入l，2，4，5处），则它在第三次跳动后， 进入5处的概率是

有人用下列方法除去硬水中某些可溶性钙、镁化合物，以降低水的硬度，你认为可行的方法是