In the context of corporate governance, explain the rules relating to the appointment, duties and powers of a company secretary in a public limited company. (10 marks)

经济型数控机床一般采用（）作为驱动执行部件

A.直流伺服电动机

B.交流伺服电动机

C.直流或交流伺服电动机

D.步进电动机