补全对话（15分）
A: Good morning! 小题1:________________________?
B: Good morning, sir! I’d like to buy a hat.
A: Who is it for , please? Is it for you , madam?
B: No, it’s for my husband.
A: 小题2:________________________________________?
B: Size 7.
A：How about this one?
B: It looks nice. 小题3:___________________________?
A: It’s made of real fur.
B: Good . __小题4:__________________________________?
A: Forty-five yuan.
B: It’s a bit expensive, but it’s really a nice hat. 小题5:______________. Here’s fifty yuan and you may take the change.
A: Thanks , madam. Goodbye.
B: Goodbye.
由关系R和S通过运算得到关系T，则所使用的运算为______。