I can think of many cases ______students obviously know a lot of English words and expressions but couldn’t write a good essay .
Your composition is written very well ______________ some spelling mistakes.
________ makes mistakes must correct them.
We must take steps to prevent the __________ world population.
The amount of money that he saved reached _________ 30000 dollars.
It is pretty well understood_______controls the flow of carbon dioxide in and out of the atmosphere today.