为了识别信号类型，常用的信号分析方法有（）和（）。
参考答案：概率密度函数，自相关函数
The novel written by the author ____ best, but five years ago no one could have imagined how
great a role he ____ in the literary world.[ ]
A. selling; was playing
B. sells; was to play
C. sold; had played
D. sells; is playing
保险利益原则的意义在于( )。 Ⅰ．防止道德风险的产生 Ⅱ．避免赌博行为的发生 Ⅲ．保证保险人的偿付能力 Ⅳ．限制保险金额 Ⅴ．保持保险人良好的信誉
A．Ⅰ、Ⅱ、Ⅲ
B．Ⅰ、Ⅱ、Ⅳ
C．Ⅰ、Ⅱ、Ⅲ、Ⅳ
D．Ⅱ、Ⅲ、Ⅳ
