Having never met with such a _____ problem, he felt _____ and didn’t know how to solve it.
— 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 .
If you ____ me , I''ll give you some advice .
Although he knew little about the large amount of work done in the field, he succeeded ________ other more well - informed experimenters failed.