We must try _____ people _____ the animals in danger.

3D printers are still _____ expensive for most of us ______ afford.

Not believing their eyes, the visitors on the spot _______ the flying plane, doing some most difficult and dangerous tricks in the sky.

In order to make our city green，______.

I know she is very ______ . Look! The smile(微笑) is on her face.