胶印机开机前不需要安装的是（）
A、安装树脂版
B、安装网版
C、安装橡皮布
D、安装墨辊
参考答案：B
It is hard to imagine a large city without policemen, but such was the ______ in London in the early 18th century.
A．condition
B．affair
C．environment
D．situation
新产品一般要经过4个阶段的生命周期，即导人期、成长期、成熟期、衰退期。( )
