The boy is old enough to __________ the difference __________ right and wrong.
The boy insisted that he __________ the glass. He said that he was not there then.
—Sorry, sir. I'm late again.—What excuse will you __________ for yourself this time?
This box __________ all the books you need, __________ an English-Chinese dictionary.
We'd better set off or it will be dark __________ we know it.
I ___________in the No.8 Middle School for three years, and I have been in this school for one and a half years.