is known to us all that the old scientist,for life is hard in the past,still works hard in his eighties.
Your article is too long. You must __________ to about 3000 words.
I've always smoked, but I'm trying to __________.
Anything __________ could be found has been used to repair the damaged bridge.
If the way __________ you think of is not good enough, you can learn the way __________ the top students deal with their study.
The doctor did __________ he can __________ the boy.