________ many times, he finally understood it.
The sign reads, “In case of _____ fire, break the glass and push _____ red button.”
We _______what our soldiers have done for our country.
They are fighting ________us _________the enemy
She’s having a lot of trouble with the new computer, but she doesn’t know whom to ________.
Tom is good at maths, so I think he is the student ______can help you to work out this problem.