Spotlight on grammar: model auxiliaries
Study the examples, and then choose the best answer to complete each sentence.
(possibility) the key to happiness may/might/ could be great relationships.
(impossibility) Some people say you can’t be happy without money.
(strong obligation) whatever the key is for you, you must try to make it happen.
(weak obligation) If you’re not happy, you should ask yourself why.
(no obligation) You don’t have to change everything immediately.