【单选题】PLC 总体检查时,首先检查电源指示灯是否亮。如果不亮,则检查 ( ) 。
【单选题】Jane_____havecome to the party, but she______not find the exact time.
【判断题】250 km/h以下铁路采用CTCS-2级列控系统。
【单选题】Every day, ______ lead to the invention of many new words to describe them.
A.
new discoveries in science and technology
【单选题】设 是一个拓扑空间, , ,点 是 的内点,则( )