用适当的介词填空
I sent a letter to Bob ________ his mother．
We are not familiar ________ the paintings painted by Picasso．
You must concentrate ________ what the teacher tells you．
He came up ________ a good plan, and we all agreed to take it．
The price for salt is going ________ these days．Let’s buy some in case the price is raised．
Our club consists mostly ________ workers．
Yang Liwei is known ________ his first travel to travel space．
Professor Li isn’t in the office ________ the moment．
句型转换
Before liberation, the labouring people had no rights to enjoy education．
Before liberation, the labouring people ________ ________ ________ ________ education．
A good idea was put forward at the meeting．
A good idea ________ ________ at the meeting．