题目内容（请给出正确答案）

[单选题]

It has been twenty years ______ the Browns settled down in China.

A.until

B.before

C.when

D.since

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第1题

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signed by the IETF to(71) the current version Internet Protocol, IP version 4("IPv4").

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A．substitution

B．swap

C．switchover

D．replace

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第2题

By the time we got to the cinema the film（）for half an hour.

A.has begun

B.had begun

C.has been on

D.had been on

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第3题

It is not necessary to state whether freight has been paid or is paid at destinat

ion．（）

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第4题

My sister has _____to Beijing twice.

A.gone

B.got

C.come

D.been

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第5题

Once the decision ____, the most important thing to do is how to carry it out.

A.has been made

B.made

C.been made

D.having been made

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第6题

___ World War Ⅱ, DDT has been used in large quantities.

A.because

B.although

C.for example

D.since

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第7题

The Smiths（）in China for 8 years.

A.has lived

B.lived

C.have been

D.live

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第8题

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第9题

Though the hotel has only been open for a few days, it is already （) booked.A．expectantlyB

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A．expectantly

B．quickly

C．heavily

D．immediately

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第10题

The “Nine-Cottage Valley” has been listed as a world natural （） by the UNESCO.

A.cultural