She thought hard for a little while ______ she began to write.

He had been a worker ______ he became a college student.　　　　

I had a long talk with our headmaster. It was very helpful ______ me.

We'll work even harder to build our country ______ a great socialist one.

It is necessary to wash one's hands ______ meals.

I have learned English ______ two years.

Mr Hopkins was ill. Mrs Green gave us a lesson ______ place of him.

Don't get ______ his way. He is very busy now.

It is important ______ people to protect birds.

I have been invited ________ the first time to such an important meeting.