21. In recent years______ global warming is becoming ______ concern for people all over the world.
A. the; the B. a; / C. /; a D. the; /
22. ______cover 29th Olympics, thousands of journalists gathered in Beijing.
A. So as to B. In order to C. In order that D. So that
23. With two children ______middle school in the nearby town now, the parents are working hard.
A. attended B. attending C. joined D. joining
