汽车发动机转速越高，蓄电池点火系中断电器触点的闭合时间就相应减少，闭合和断开的频率就增高，导致次级电压也就越高，点火性能就越好。
参考答案：错
He _______ in a university for five years, but now he runs a company of his own.
A．has taught
B．had taught
C．taught
D．has been teaching
信息系统的开发可采用多种模式： Ⅰ．委托开发 Ⅱ．合作开发 Ⅲ．自行开发 上述哪(些)种开发方式最有利于用户对系统的维护
A．Ⅰ
B．Ⅱ
C．Ⅲ
D．Ⅱ和Ⅲ
