How much is this dress It is on sale____20% off.A on B for C at 应填哪个选项 ,why

问题描述:

How much is this dress It is on sale____20% off.A on B for C at 应填哪个选项 ,why

B

Is this chair on sale for only 15 yuan?
这把椅子在低价销售只卖15元吗?
on sale for接多少钱,指以什么价格出售。

正确答案:
C.at 20% off.
如选择B,则后面要跟价格,如:for $20.
A是不可取的,只是搭配的问题.
除定冠词之外,英语的介词是最难学的,只能根据习惯用法强击,到时就熟能生巧了.往往没有“why”可言.