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听力原文：W: I'll be late. I'm due at work at 9:00 sharp.
M: Don't worry. You've got plenty of time. You still have five minutes.
Q: What time is it now？
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The network layer provides services to the transport layer．It can be based on either (1)．In both cases，its main job is (2) packets from the source to the destination．
In network layer，subnets can easily become congested，increasing the delay and (3).
for packets．Network designers attempt to avoid congestion by proper design．Techniques include (4) policy，caching，flowcontrol，and more．
The next step beyond just dealing with congestion is to actually try to achieve a promised quality of service．The methods that can be used for this include buffering at the client，traffic shaping，resource (5)，and admission control．Approaches that have been designed for good quality of service include integrated services(including RSVP) ，differentiated services， and MPLS．
(1)
W: Yes, it was fantastic. Now I know why it is listed together with the Nile River as one of the great natural wonders of the world. Here, want to see the pictures I took？
M: Oh, what a view! It's even bigger than I had imagined. I remember reading about the Grand Caoyon and I think it is said that it was formed suddenly when the earth's crust split open during an earthquake.
W: Well, not that quickly. Look, here is the picture 9f the Colorado River. See way down at the bottom of the canyon. That river and its tributaries have been weaving the canyon floor away for 10 million years.
M: Then the canyon is the result of swell erosion. I'll bet geologists have made some interesting discoveries there.
W: Not only the geologists, archaeologists have found the 5ones of extinct animals in caves in the canyon walls. In a cave one hundred and forty feet above the river, they found driftwood that dates back as far as 37 thousand years.
M: That means the river must have been a hundred and forty feet higher up when it carried the driftwood into the cave.
W: It's very possible, but, of course, who knows？ The Grand Canyon is full of mystery. Wouldn't you like to go the Arizona someday？
M: You bet I would.
Where has the woman been？
A．Americanize the restaurants.B．Increase its advertising coverage to the rich.C．Focus
Under the new scheme an EEC driver wanting to live and drive a bus/lorry in Britain would
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