估计楼主中间漏打了一些东西,凭感觉补上一点,请勿怪!
A:What con I do for (you)?
B:Yes,(please).I want a kilo of fish.
A:OK.(Here) you are.
B:How (much) are they?
A:3 yuan.Is that (all)?
B:No,(I want)/(I'd like)some tomatoes.
A:(How many) do you want?
B:Two.
A:OK.Here you are.
B:(Thanks) a lot.
A:It's (my pleasure).