给煤机的结构特点？
参考答案：
配有微机控制，可实现高精度的煤量称重和速度自动控制。
When I went to their house, there was no light on. They _____ at home.
A．can’t be
B．couldn’t be
C．can’t have been
D．mustn’t have been
“吾见百家春秋”这句话说明“春秋”在当时是史书的统称。
