式子(-1)2007+(-1)2008的值为( )
A.-1
B.-2
C.0
D.1
(-1)2007+(-1)2008=-1+1=0.
故选C.
已知一组数据:8,6,10,13,15,8,7,10,11,12,10,8,9,11,9,12,10,12,11,9。如果取组距为2,这组数据应分( )组。
In the past three years they _ nothing. [ ]
A. do
B. did
C. had done
D. have done