He treated me as though/as if _____ his own son.

There is no simple answer，________is often the case in science

Do you know ________ tall girl in purple–Sure. That’s Kate. She is an old friend of mine.

Mr. Wu found that a number of UFOs in the sky ______ in a very short time in surprise.

How are you getting along with your studies—-I haven’t made ________I should.