由高挡换入低挡后，若发动机牵阻力突然增大，车速骤降，说明换挡时机（）。
A、过早
B、过迟
C、适中
D、不当
参考答案：A
—Karl Marx was born in Germany and German was his native language.
—________, as far as I know. [ ]
A. So was Engels
B. It was the same with Engels
C. So Engels was
D. Neither was Engels
能反映急性胰腺炎病情严重程度和预后的指标是（）
A.血清淀粉酶
B.尿淀粉酶
C.血清钙
D.血清镁
E.血清钠
