例句： He was depressed by his defeat.

例句： There's an ink stain on your shirt.

例句： The discovery of how bronze is made was probably accidental, but it turned out to be an important event.

例句： She fought like a tiger to get what she wanted.

例句： It's the job of the church to help people lead better lives.

例句： I heard she got married.

例句： The answer to his problem was staring him in the face.

例句： It's my habit to take a nap at noon.

例句： Litmus paper can be used as an indicator of the presence of acid in a solution.

例句： distributing handbills on the street.