正常成人在清醒、安静和闭眼放松情况下，ECG枕部和顶部主要为：（）
A.α波
B.β波
C.θ波
D.δ波
参考答案：A
维生素D缺乏性手足抽搐症有哪些临床表现？
George would certainly have attended the meeting，__________.
A．if he didn’t get a flat tire
B．if the flat tire hadn’t happened
C．had he not had a flat tire
D．had the tire not flattened itself
