诊断高血压心脏病必须具备的先决条件是
A．心绞痛B．心律不齐C．左心室肥厚D．右心室扩大E．心力衰竭
参考答案：C
The story _______ I read in the newspaper was about a common problem among teenagers. [ ]
A. whose
B. who
C. that
D. where
使用中电动机容量选择太小，会发生（）。
A、功率因数变低
B、超载运行，影响寿命
C、功率因数提高
D、转速降低
