The two things are the same in outward formbut different _____.

My new novel has disappeared.Who _______ have taken it?

My son prefers us to email each other once a week spend half an hour on the phone every night.

He failed the exam again！What should I do，Miss Wang—In my opinion，your son is________than stupid

The family is a cooperative enterprise for which it is difficult to _____ rules, because each family needs to work out its own ways to deal with its own problems.