A．机械能转化为电能
B．电能转化为机械能
C．热能转化为电能
D．电能转化为热能
答案：B
It is surprising that Jack, who is only 39 years old, _______ in the field of engineering for 20 years when he entered the company last month.
A．worked
B．had worked
C．has worked
D．working
在设计程序时，应采纳的原则之一是______。
A．程序结构应有助于读者理解
B．不限制goto语句的使用
C．减少或取消注解行
D．程序越短越好
