21. With the help of curriculum reform, students enjoy a variety of after-school activities, ______ up to half are aimed at strengthening their physical strength and building up their confidence.
A. to which B. of which C. from which D. in which
22. —When shall we set about doing our work?
—______ all the group members are here.
A. Until B. Since C. Unless D. Not until
23. They ___________with joy when they heard that their class won the first place in the relay race.
A. sprang up B. split up C. took up D. picked up
