幼年型类风湿性关节炎(JRA)的病理改变有()
A.关节周围肌腱炎
B.关节骨膜炎和骨质疏松
C.胸膜炎
D.心包炎
E.虹膜睫状体炎
参考答案:A, B, C, D, E
His failure in the experiment suggested that he ________ his teacher’s proper instructions.
A.should not have followed
B.should not follow
C.mustn’t have followed
D.hadn’t followed
请简述谐波对电力系统有何危害。