By the time we reach that page, we ___________ twenty lessons of the book.
It is said that the temperature is unusual mainly _______ global warming caused by human activities.
The transformation of our city will make _______ for people here to have a comfortable environment.
Mary _______ her mother with the housework, but she didn’t.
The local government announced that only when the fire was under control ________ to return to their homes.
He left home without saying a word, and _______ worries many people and is to be found out.