How often do I need to feed the birds—They ________ food every day，or they will behungry.

s _____ a great deal of money, hoping that she can travelaround the world after she retires

I ran all the way to the post office, only ___ that it had closed.

My son is _____ to be seen. Where has he gone? — I think he _____ in the building.

Our foreign trade has________greatly in recent years .