Inside the computer, the operation system (of another software module called a data communication (71) )must decide which program will get control next. Each program remember, is associated (72) . a particular front -end port. If a program’s data have not yet reached its front - end buffer, there is no point giving that program control. Thus the data communication monitor sends its own (73) signal to the front -end devices next port is polled. Note that the (74) computer speed. The computer never has to wait for a terminal or a communication line. Instead, it is the expressive front - end processor that waits for the slower system (75) to respond.

（74）处填（）。

A．great

B．huge

C．mainframe

D．large

综合布线相对于传统布线具有很多优点，传统的布线是根据各个单独系统满足不同应用需要而设计和安装的，因此带有致命弱点，下列叙述正确的是（）。

A、系统兼容，各子系统分别独立设计，各系统互不关联，互不兼容

B、设备相关性差，各系统的终端设备只在本系统内有效，超出本系统不被支持

C、工程协调难，工程施工分别进行，因而难以协调，造价高，工程完工后统一管理较难

D、灵活性差，缺乏统一的技术标准和统一的传输介质，系统一经确定便难以更改，灵活性差