— What on earth are the police busy with?— They _____into how the plane crash came about.
The children went home from the grammar school, their lessons __________ for the day.
__________ by a greater demand of vegetables, farmers have built more green houses.
The flowers his friend gave him will die unless __________ every day.
Please remain __________ until the plane has come to a complete stop.
Jenny hopes that Mr. Smith will suggest a good way to have her written English __________ in a short period.