综合布线系统的主要功能是什么？它由哪些子系统组成？
参考答案：
建筑物综合布线系统（PDS）又称为开放式布线系统，它是建筑物或建筑群内部之间的传输网络。它将建筑物内部的语音交换设备、智能数据处理设备及其它数据通信设施相互连接起来，并采用必要的设备与建筑物外部数据网络或电话线路相连接。综合布线系统一般由下列六个独立的子系统所组成工作区子系统、水平布线子系统、管理子系统、干线子系统、设备间子系统、建筑群子系统。
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| Where's salt from? In the northwest of our country there are __1__ salt lakes. Some __2__ them are very big. The salt in a big lake can meet the needs of our people for __3__ to come. But __4__ of the salt in our country is from the sea. Great holes are dug and __5__ the sea water. When the sun dries up the water, salt can be got __6__ the ground. The salt is white and clean __7__ beautiful. We can't live __8__ salt. we need it in our food. __9__ need it, too, salt is very important __10__ us. | ||||
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