21.   ---It’s too hard.I can’t figure it out, Mommy.
--- _______, Tommy.You can make it!
A.No problem      B.No hurry           C.Come on            D.That’s OK
22.By awarding the Nobel Peace Prize to Mr.Obama,       Nobel Committee surely hoped to influence _____debate about U.S.policy in Afghanistan.
A.a; the                  B.a; a                     C.the; the               D.the; a
23.I can’t help      if my students are always making any noise in class.
A.this                     B.that.                    C.them                   D.it