The form ______in and returned within three weeks.

The old man came         to the  railway station，only          the train was slowly pulling out of the station．

After walking on the zigzag path to the mountain top for a few hours, the tourists gathered under trees_____ shade and______ down to have a rest.

The novel is so interesting that it is worth ________ another time.

With a lot of difficult problems_____, the newly-elected president is having a hard time.