直流电动机有哪几种调速方法？各有哪些特点？
参考答案：
调压调速，弱磁调速，转子回路串电阻调速，变频调速。特点略。
---I don’t want to go to school on foot. What should I do?
---You try asking your father for a bike, or you can go by bus.
A．have to
B．must
C．might
D．can’t
8259A通过级联的方式可以由几片构成最多多少级优先权的中断源？
