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问题 选择题
1-tan27°tan33°
tan27°+tan33°
等于（　　）
A．
3
3
B．
3
C．tan6°D．
1
tan6°
答案

因为

1-tan27°tan33°
tan27°+tan33°
=
1
tan(27°+33°)
=
1
tan60°
=
3
3
．

故选A．

选择题
下列各式：①-
x
2
，②-
y
2x2
，③
y
π-1
，④
y2-1
(x-1)2
，其中是分式的有（　　）
A．1B．2C．3D．4
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单项选择题

In low-speed network，it is usually adequate to wait for congestion to occur and then react to it bytelling the source of packets to slow down．In high-speed networks，this approach often works poorly，because in the (71) between sending the notification and notification arriving at the source，thousands of additional (72) may arrive．In ATM network，a major tool for preventing (73) is (74) control．When a host wants a new virtual (75) ，it must describe the traffic to be offeredand the service expected．

（74）处填（）。

A．flow

B．admission

C．traffic

D．time
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