It is impossible for ______ little children to do ______ much work in ______ a short time.
The company __________ a rise in salary for years, but nothing has happened.
I'm glad to see that you __________ a lot of progress since I__________ you last.
—Did you find the missing couple in the mountain yesterday? —No, but we __________ to get in touch with them ever since.
__________ my sister three times today but her line was always busy every time I phoned her then.
She ought to stop working, she has a headache because she __________ too long.