在一棵树中，（）没有前驱结点。
A.分支结点
B.叶结点
C.树根结点
D.空结点
参考答案：C
With so many friends _____ me, I had no difficulty finishing the work on time. [ ]
A. to help
B. helped
C. helping
D. have helped
采用电子计算机进行会计核算的单位，应当保存打印出的纸质会计档案。( )
