The arbitrage-free bond valuation approach can best be described as the:（）

A. use of a single discount factor.

B. use of a series of spot interest rates that reflect the current term structure.

C. arithmetic average of the spot interest rates.

普萘洛尔具有较强的β受体阻断作用，对β1和β2受体的选择性很低。可使心肌收缩力和心排出量减低，冠脉血流下降，血压下降，窦性心率减慢。因此答案为C（）。

A.奎尼丁

B.肾上腺素

C.普萘洛尔

D.哌唑嗪

E.维拉帕米