A:Excuse me ,what can I do for you ?
B:I want to buy two pens .
A:How about this red one and green one ?The quality is good and they are also cheap.
B:how much are they?
A:Twenty yuan in total .And if the pen have some problems ,you can change it in free .
B:OK!I will take them. 不知你是几年级
求采纳