II.单项填空(共15小题;每小题1分，满分15分)
21. –Do you know who invented _______ telephone?
- No, but it is really _______ most useful invention.
A. the; / B. a; a C. the; a D. a; the
22. If we don’t take some measures to protect this kind of plant, it will ____ soon.
A. die out B. die down C. die from D. die of
