双馈电机为什么被称作“双馈”？
参考答案：
因为双馈电机在运行时，转子与定子可同时向电网输送电能。
普萘洛尔阻断交感神经末梢突触前膜上的β受体，可引起
A．去甲肾上腺素释放减少
B．去甲肾上腺素释放增多
C．心率增加
D．心肌收缩力增强
E．A－V传导加快
用所给单词的适当形式填空。
1. You must think about _____ (person) safety.
2. The children might hurt _____ (them) if they walk alone.
3. Are you careful or _____ (care)?
4. The classroom is very _____ (noise) before the teacher came in.
5. He is so _____ (friend) to others.
