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问题 选择题
项数为n的数列a1，a2，a3，…，an的前k项和为Sk（k=1，2，3，…，n），定义
S1+S2+…+Sn
n
为该项数列的“凯森和”，如果项数为99项的数列a1，a2，a3，…，a99的“凯森和”为1000，那么项数为100的数列100，a1，a2，a3，…，a99的“凯森和”为（　　）
A．991B．1001C．1090D．1100
答案

∵项数为99项的数列a1，a2，a3，…，a99的“凯森和”为1000，

∴

S1+S2+…+S99
99
=1000，

∴100，a1，a2，a3，…，a99的“凯森和”为

100+100+S1+100+S2+…+100+S99
100
=100+
S1+S2+…+S99
100
=100+990=1090，

故选C．

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．limited

D．imprison
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单项选择题

起管柱过大的（）能造成溢流、井涌。

A、激动压力

B、井口回压

C、抽汲压力

D、井底压力
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