If you _____________ your study, I am sure you will make greater progress.
He hid himself behind the door _____ he still could see what would happen to his classmates.
Do you have any idea of the reason _____ he referred to?
They stayed up until midnight _____ the old year out and the new year in.
If the car won’t start, _____ it.
“Which sweater is yours?” “The one _______ No. 9.”