(     ) 6.You may go fishing if your work _______ .

       A: is done   B: will be done   C: has done   D: have done

(     ) 7. There used to be a river in front of the village, ______ ?

       A: did it     B: usedn’t it     C: didn’t there   D: did there

(     ) 8. China’s 24^th science research team _____ at Changcheng Station on

         January 5, 2008.

       A: have arrived ; improve    B: arrived ; has improved

       C: arrived ; have improved   D: have arrived ; have improved