21. Believe it or not. It often takes four hours to get my electric bike fully_____ .
A. conducted B. charged C. functioned D. operated
22. Help others whenever you can______ you will make the world a nice place to live in.
A. and B. or C. unless D. but
23. At the meeting they put forward a new method, which______ highly effective.
A. proved of B. proved
C. proved that D. was proved that
