在vi中，不对文件做修改，强制退出，按（）。

A、x键

B、q!键

C、q键

D、esc键

通信管道、通道与铁路钢轨（或坡脚）的最小平行净距为（）m。

A、2

B、1.5

C、1

D、0.5

Which two statements about sequences are true? （）

You use a NEXTVAL pseudo column to look at the next possible value that would be generated from a sequence, without actually retrieving the value.

You use a CURRVAL pseudo column to look at the current value just generated from a sequence, without affecting the further values to be generated from the sequence.

You use a NEXTVAL pseudo column to obtain the next possible value from a sequence by actually retrieving the value from the sequence.

You use a CURRVAL pseudo column to generate a value from a sequence that would be used for a specified database column.

If a sequence starting from a value 100 and incremented by 1 is used by more then one application, then all of these applications could have a value of 105 assigned to their column whose value is being generated by the sequence.

You use REUSE clause when creating a sequence to restart the sequence once it generates the maximum value defined for the sequence.

一个工程师在同一个ATA上面，安装两个IDE硬盘，第一个硬盘跳线设置为Master，BIOS检测到它，第二个硬盘跳线设置为Slave，但是BIOS不能检测到它，那么下一步该如何解决这个问题？（）

A、换第一个硬盘

B、换第二个硬盘

C、把CD-ROM设置为Slave设

D、置第二个硬盘为Master

管道铺设应有一定的坡度，以利渗入管内的地下水流向人孔。下列（）管道坡度符合要求。

A、2‰

B、2.5‰

C、3‰

D、3.5‰

直放站提取信号源的主要方式有哪几种：（）

A、通过直放站的施主天线直接从附近基站提取信号。

B、用耦合器从附近基站耦合部分信号通过光纤传送到盲区内的直放站。

C、通过直放站的施主天线直接从附近直放站提取信号。

D、用耦合器从附近基站耦合部分信号通过电缆传送到盲区内的直放站。