---What on earth are the police busy with? ---They have been looking into how the plane crash _______.

He was persuaded by the doctor to _____ smoking.

After he gave a report about the school, Mr White____ the visitors around it. 

–When did the concert_____?---Oh, two days ago.

 An artist who was recently traveling on a ferry to the southern island discovered ________ a long lost antique Greek vase.