两台打夯机前后操作时的间距不小于（）m。
A、20
B、10
C、9
D、8
参考答案：B
26．Nowadays people have to pass various tests for professional __________ so that they can be qualified for a well-paid job.
A．certificates
B．permission
C．admission
D．Perseverance
在配电设计中，通常采用（）的最大平均负荷作为发热条件选择电器或导体的依据。
A.10min
B.20min
C.30min
D.60min
