.When ___ help, one says “Thank you” while when _________ help, one asks “Can I help you?”
________ private cars are bringing us convenience, they may also cause more traffic accidents and pollution.
In no case _______ go _______ the law of nature or we’ll meet endless suffering.
— How do you know so much about what’s going on in the countryside?— I’ve got a friend there who keeps me ________.
If the firefighters ________ in time, the fire would have resulted in many deaths in the hotel.
_________ development of nuclear weapons is _________ threat to mankind.