给水管道的位置、标高、支吊架安装、分户验收时应（）。A.全数检查 B.检查数量50%

一木箱放在平板车的中部，距平板车的后端、驾驶室后端均为L=1.5m，如图所示处于静止状态，木箱与平板车之间的动摩擦因数为μ=0.5，现使汽车以a₁=6m/s²的加速度匀加速启动，速度达到v=6m/s后接着做匀速直线运动，运动一段时间后匀加速刹车求：

（1）当木箱与平板车的速度都达到v=6m/s时，木箱在平板车上的位置；

（2）刹车时为保证木箱不会撞到驾驶室，刹车时时间t'至少应为多少？（g=10m/s²）

联结若干独立企业法人形成企业集团的纽带是（）。

A.产品

B.资产

C.技术

D.政府

以下关于商业区的说法，正确的是

A．商业区只分布在城市中心，呈块状分布

B．中心商务区是城市经济活动最繁忙的地区

C．商业区是城市内所有商业集中分布的地区，商业区内只有商业活动

D．便利的交通能吸引大量的消费人口，因此在交通线上都会形成商业区

A transport layer protocol usually has several responsibilities. One is to create a process-to-processcommunication UDP uses ______ numbers to accomplish this. Another responsibility is to provide controlmechanisms at the transport level, UDP does this task at a very minimal level. There is no flow control mechanismand there is no ______ for received packet. UDP, however, does provide error control to some extent. If UDPdetects an error in the received packet, it will silently drop it.
The transport layer also provides a connection mechanism for the processes. The ______ must be able to sendstreams of data to the transport layer. It is the responsibility of the transport layer at ______ station to make theconnection with the receiver chop the stream into transportable units, number them, and send them one by one. Itis the responsibility of the transport layer at the receiving end to wait until all the different units belonging to thesame process have arrived, check and pass those that are ______ free, and deliver them to the receiving process asa stream.

A．jobs

B．processes

C．programs

D．users

堤防滑坡易在堤脚处或其附近有（）现象。

A.凹陷

B.沉陷

C.隆起

D.变陡