根据对话内容，补全对话

A: What can I do for you?

B：I want to buy a pair of shoes.

A:____

B: Size eight or nine.

A: Ok! How about this pair?

B: Sorry, I do not like black.____

A: Yes. We have blue, white and brown ones .

B: Can I havea look at the brown ones?

A: Yes, please.

B: ____

A: Forty-sixyuan.        

B: It is too expensive. ____

A: How about forty?    

B: It is still expensive. What about thirty-five?

A: All right.

B: OK.____

1998年，科学家在南极洲发现大量的企鹅死亡，经解剖检验发现其体内含有超量的氢化物和其他大量有毒物质，下列不是造成此后果的原因是（   ）