实验用狗首选的麻醉方法是（）
A.吸入麻醉
B.静脉麻醉
C.皮下麻醉
D.肌肉麻醉
E.腹腔麻醉
参考答案：B
–A boy was killed by the tiger in the zoo.
–He was believed into the cage while feeding the tiger without permission.
A．to fall
B．to be falling
C．to have fallen
D．having fallen
变频器主要由整流器、中间直流环节、逆变器和______组成。
