在TCP/IP互联网络中，转发路由器对IP数据报进行分片的主要目的是( )。
A．提高路由器的转发效率
B．增加数据报的传输可靠性
C．使目的主机对数据报的处理更加简单
D．保证数据报不超过物理网络能传输的最大报文长度
参考答案：D
解析： 由于利用IP进行互联的各个物理网络所能处理的最大报文长度有可能不同，所以IP报文在传输和投递的过程中有可能被分片，从而保证数据不会超过物理网络能传输的最大报文长度。
Directions: There are four passages in this part. Each of the passage is followed by five questions or unfinished statements. For each of them there are four choices marked A, B, C and D. Choose the best one and mark your answer on the ANSWER SHEET with a single line through the center.
Passage One
| When TV news programs report wars or disasters, the editors rarely use the most horrifying pictures of dead or wounded victims because they don’t want to upset their viewers. Even so, viewers are usually warned in advance that they "may find some of these scenes disturbing", so they can look away if they choose. But the men and women whose job is to record those scenes — the TV cameramen — have no such choice. It is their duty to witness the horrors of the world and record them no matter how gruesome and unpleasant they may be. Consequently, it is one of the most dangerous, exposed and emotionally taxing jobs the world has to offer. Today, the demand for their work is rising, the explosion of satellite broadcasting and 24hour news in recent years has created an almost insatiable demand for TV information. But major broadcasters and TV news agencies — such as Reuters and WTN — have never had enough staff to meet the worldwide demand for up-to-date pictures, so increasingly they turn to "freelance" TV cameramen. These freelance cameramen are independent operators tied to no particular organization. They will work for any company which hires them, be it for just a few hours or for several weeks in a war zone. But if the freelance cameraman is injured, in the course of the job, the TV company is not responsible for him. The freelancer must survive on his own. "TV will always need hard, vivid moving pictures which are fresh, but these companies feel uncomfortable with large numbers of employees on their books," explains Nick Gowing, once foreign editor for Britain’s Channel 4 news and now a BBC presenter. "By hiring freelancers, they can buy in the skills they need only when they need them. It also enables them to contract out the risk," he says. |
The main idea of the first paragraph is that ______.
A．it is the duty of TV cameramen to record horrifying scenes
B．TV cameramen’s job is extremely dangerous and emotionally taxing
C．TV programs are reducing the use of horrible pictures of death and wound
D．it is a requirement by work for TV cameramen to disregard people’s wound