运行速度大于140km/h的由机车牵引的列车在提速半自动闭塞区段采用速度分级控制方式。
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You create the sales report and run it in the live previewer. After which change would the live previewer require the data? （）
A. Removing column from the available list in the report wizard.
B. Removing the column from the displayed list in the report wizard.
Changing the display width of a column in the report wizard.
D. Adding a column to both the available list and displayed list in the report wizard.
E. Removing a column in the live previewer.&e
若使晶体三极管工作在（）状态，必须使发射极加负偏压或零偏压，即使基极电流小于零，此时集电极一般也承受负偏压。
A. 放大状态
B. 截止状态
C. 饱和状态
喷油试验一般在机组空负荷状态下进行。
A. 正确
B. 错误
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