---Must I work out the problem right now?---Yes, you _______. It’s very serious. 

–What do you think we can do for our parents? --You ____ do anything except to show your love -- a kind word, a warm smile and a helping hand.

Delta, the American airline, is sometimes jokingly explained “Don’t expect your luggage to arrive” because it ______ be very slow.

 We all know that we ________ our carbon footprint, but I suspect that many people wouldn't be prepared to go as far as Joan Pick, a retired scientist living in south London.

—Look at the picture on the wall. It ________be David’s.—Yes, his name is on the first page.