安全边际部分的销售减去其自身变动成本后称为企业利润，即安全边际中的边际贡献等于企业利润。 ( )
参考答案：对
— I have failed. I really don't know why I did so badly.
—________ Just try to do it better next time.
A．Look out！
B．Don't lose heart！
C．You're hopeless.
D．Can't you be more careful?
Esomolol是一种静脉用的短效β-受体阻滞剂，可用于下列哪些情况（）
A.房性心动过速
B.非预激性房颤或房扑
C.心肌缺血
D.异常窦性心动过速
E.尖端扭转性室速
