There is no way of knowing why one man makes an important discovery ______ another man, also intelligent, fails.
He studied hard and ____ pass the examination .
The money was soon spent , so he ____ go hungry .
— Would you open the window , please ? — Yes , I ____ .
I''m surprised that he ____ to help me when I needed his help .
A lion ____ only attack a human being when it is hungry .