People have always been_______aboutexactly how life on earth began

isn’t going to be a volleyballmatch next week, __________

How much do I owe you for lunch—– ______ . It’s nothing.

(2013·高考天津卷)If you are in trouble，Mike is always willing to ________a hand

Could you meet me at the airport— I’d like to，but I’m afraid I ______ a very important meeting when you return.