What on earth are the police busy with— They have been investigating how the train crash __________.

With the work ____, Mr Lin went out for a swim [ ]

What happened while Linda was______ the telephone

Do you think we can get there on time -Yes，_______ the truck doesn’t break down.

Have you seen _________ TV series Nirvana in Fire (《琅琊榜》), Mum— Yes, it’s quite _________ interesting play, so I have seen it twice.