Investigators are still trying to determine the __________ of the accident.
Professor White has written some short stories, but he is _________ known for his plays.
Ladies and gentlemen, please fasten your seat belts.The plane ________.
.He is always ready to help others, seldom, ______, refusing them when they turn to him.
---Excuse me.Can you spare me a few minutes? ---______.
Living in such a high mountain _________be cold.