21. I was searching for ________information on ________ Internet when suddenly the power was off.
A. an; an B. an; the C. /; the D. /; /
22. Our headmaster explained to ______ that the meeting was delayed (耽误) because of the bad weather.
A. present everyone B. everyone presented C. everyone present D. presented everyone
23. Many of the earth’s plants and animals have already ______, and many other species are endangered.
A. died out B. left out C. watched out D. stood out
