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问题 选择题

压路机后轮的半径是前轮半径的3倍，A、B分别为前轮和后轮边缘上的一点，C为后轮上的一点，它离后轮边缘的距离是后轮半径的一半．则A、B、C三点的线速度的比值是（　　）

A．2：2：1

B．1：2：1

C．1：2：2

D．1：1：2

答案

A、B分别为同一传动装置前轮和后轮边缘上的一点，

所以VA=VB，

因为rA：rB=1：3，所以ωA：ωB=3：1；

B、C两点共轴，所以ωC=ωB ．

所以ωA：ωB：ωC=3：1：1；

根据v=ωr得：

vA：vB：vC=2：2：1

故选A

选择题

______ intelligence, you are no worse than others. It is your attitude that makes the greatest difference.

A．Regardless of

B．In terms of

C．In case of

D．On top of
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单项选择题

The network layer provides services to the transport layer．It can be based on either (67) ．In both cases，its main job is (68) packets from the source to the destination．

In network layer，subnets can easily become congested，increasing the delay and (69) for packets．Network designers attempt to avoid congestion by proper design．Techniques include (70) policy,caching，flow control，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，trafficshaping，resource (71) ，and admission contr01．Approaches that have been designed forgood quality of service include integrated services(including RSVP)，differentiated services，andMPLS．

71（）

A．distribution

B．reservation

C．scheme

D．guarantee
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