23.Play, often seen as        activity for kids, is still important in         development of teenagers.
       A.the; the               B.an; the                C.an; 不填             D.the; 不填
24.      alone in the large house, the little boy had to learn to survive by himself.
       A.To leave              B.Leaving               C.Left                    D.Being left
25.On snowy days, you have to drive very        to avoid traffic accidents.
       A.cautiously           B.neatly                 C.smoothly             D.properly
26.The time is drawing near         food raised in space will directly benefit humans below.
       A.where                 B.when                  C.whether               D.why