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问题 单项选择题

风速20m/s的均匀气流，横向吹过高H=40m，直径d=0.6m的烟囱，空气的密度ρ=1.29kg/m3，空气的运动黏滞系数v=15.7×10-6m2/s，绕流阻力系数CD=0.4，烟囱所受风力为（）。

A.2477N

B.3134N

C.4450N

D.4988N

答案

参考答案：A

解析：

绕流阻力为

单项选择题

IPv6 is short for "Internet Protocol Version 6". IPv6 is the "next generation" protocol designed by the IETF to ( 71 ) the current version Internet Protocol,IP Version 4("IPv4").
Most of today’s Internet uses IPv4, which is now more than twenty years old． IPv4 has been (72) resilient in spite of its age, but it is beginning to have problems. Most importantly, there is a growing ( 73 ) Of IPv4 addresses，which are needed by all new machines added to the Internet.IPv6 fixes a number of problems in IPv4，such as the (74) number of available IPv4 addresses. It also adds many improvements to IPv4 in areas such as routing and network autoconfiguration.IPv6 is expected to gradually replace IPv4，with the two coexisting for a number of years during a transition (75) .

A．restrict

B．confine

C．1imited

D．imprison
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单项选择题

珠穆朗玛峰海拔8844.43m，下列说法（）正确

A.珠穆朗玛峰顶到假定水准面的铅垂距离为8844.43m

B.珠穆朗玛峰顶到青岛国家水准原点的铅垂距离为8844.43m

C.珠穆朗玛峰顶的相对高程为8844.43m

D.珠穆朗玛峰顶与青岛国家水准原点的高差为-8772.17m
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