______ it got dark, they still worked hard there. [ ]
A. Though
B. If
C. Since
答案:A
某等距连续变量数列,其末组为开口组,下限为900,又知其邻组的组中值为860,则末组组中值为()。
A.840
B.860
C.940
D.960
在鱼种越冬并塘前,停止投喂应在并塘前()
A.1天
B.2天
C.一周左右
D.二周左右