The article written by the famous economist is really _______. None of us can understand it.

－What do you think of the pollution－______ it’s serious, everyone can do something to save the world.

Mr. Black often goes to work by______ bus.

Hearing her only son killed in the accident, the old woman ________ her face in her hands and cried.[ ]

Do you mind my smoking here—________. Look at the sign. It says, “No smoking.”