The officer gave orders that anyone_____ a gun should be reported to the police station.

The doctor has worked with patients of this kind for eight years, so he knows what ________ in his job.

_______ on the American Civil War, the book attracted a large number of readers when it was published.

 _________working all day long, he fell asleep as soon as he lay on the bed.

In the job interviews, job applicants often find themselves ________ unexpected questions, some very difficult to answer.