Although there is air around us,____we can not see it.
A、but B、yet C however D、then
改写句子，
原句As he had been asked to lecture in Shanghai,Mr Whitewas unable to come
改：Mr White ____________,so_________.
原句：No sooner had the bell rung than we reached the school.
改：Hardly__________________.
原句：By the time he graduated from the middle school,he joined the Youth League.
改：He_________just before___________.
原句：Work done ,they left for the cafe.
改：As_______________.
原句：He needed the money himself but he lent it to his friend.
改：Although______________________.
原句：Weather permitting ,they will go outing.
改：If_____________
B although，“尽管”，引导了让步状语从句，后面的句子就是主句；yet，“然而”，副词，修饰整个句
子。
原句As he had been asked to lecture in Shanghai,Mr Whitewas unable to come
改：Mr White had been asked to lecture in Shanghai，so he wasn't able to come。
原句：No sooner had the bell rung than we reached the school.
改：Hardly had the bell rung when we reached the school。
原句：By the time he graduated from the middle school,he joined the Youth League.
改：He graduated from the middle school just before he joined the Youth League。
原句：Work done ,they left for the cafe.
改：As work had been done，they left for the cafe。
原句：He needed the money himself but he lent it to his friend.
改：Although he needed the money himself ， he lent it to his friend。
原句：Weather permitting ,they will go outing.
改：If the weather is fine，they will go outing。