People felt ________impossible for man to fly into outer space some years ago.

It is said that bad living habits as well as dirty surroundings, stuffy rooms and some other factors _____ the wide spread of H1N1.[ ]

There is ____ “f” and ____ “u” in the word “UFO”.

Is that woman Ms. Zhang— ________. She’s my aunt.

Nancy reminded me of what I should ________ have forgotten