Who ______ it be that is singing in the next room?— It _______ be Lucy, but I am not sure.

The mother looked at the door _______，expecting the children’s coming

____ happens to the trees once the parties are over.?

There is usually ________ in summer inYangzhou, it helps crops(庄稼) grow well.

Confronted with the complex international situation, we need a foreign policy that is more ____.