栈通常采用的两种存储结构是线性存储结构和______结构。
参考答案：链表存储
I'm sorry, I _____ go now. My father told me on the phone that my mother was ill. [ ]
A. can
B. may
C. have to
D. could
柳丁来电是一款集（）于一身的多功能通讯增强绿色软件
