沥青的再生是沥青老化的逆过程。在已老化的旧沥青中加入再生剂，以改善()。
A.胶体结构
B.流变性
C.温度稳定性
D.安全性
参考答案：B
---The president _____ by his doctor today that his cancer has come back.
A．informs
B．has informed
C．has been informed
D．is being informed
与吸入麻醉药相比，静脉全麻药的突出优点是（）
A.效能强，麻醉效果好
B.镇痛效果好
C.起效快
D.苏醒快
E.并发症少
