On the annual International Volunteers Day, the world _____ the work of millions of people who give their time to help others.
That tree, __________ are almost bare, is a very old one.
The reason ____ she was absent is _____ he was badly ill yesterday.
It suddenly _____ to the detective that the professor was probably murdered by his own wife .
---What made her unhappy? ---_____.
The machine might break down someday in the future, ____, you can dial this number for help.