A what are you doing
B I'm looking for my pen.But I( can't )find it.
A you can borrow mine.
B Thanks o lot.But I must （buy）one in the shop.
A (Which) shop?
B The one over there.Could you go with ( me
A Certainly.
C ( What)can i do for you?
A I want a pen please.
C OK.( Here )you( are ).
A Thank you.( How )( much )is it?
C It's four yuan.Is that ( all
A Yes.Thank you.Good-bye!
C Bye
不明白的再问哟,请及时采纳,多谢!