煤属于（）。
A、岩浆岩
B、沉积岩
C、变质岩
D、大理岩
参考答案：B
The most relevant definition for duration is:（）
A. the first derivative of the security's price.
B. a security's price sensitivity to changes in yield.
C. the weighted-average time until receipt of the present value of cash flows.
挖补、剪贴法变造文书其特点是什么？
