特高压直流工程中直流滤波器保护动作后闭锁直流的有（）。
A.过负荷
B.差动保护
C.高压电容器不平衡保护
D.失谐监视
参考答案：B
The first textbooks ______ for teaching English as a foreign language came out in the 16th century.
A．to be written
B．written
C．being written
D．having written
《金匮要略》指出痉病的主脉是（）
A.脉浮而弦
B.脉浮而缓
C.脉沉而细
D.脉紧而弦
E.脉沉而数
