[单选题] ________ is known to the world,Mark Twain is great American writer.

1、[单选题]The water will be further polluted unless some measures ______

• A、will be taken
• B、are taken
• C、were taken
• D、had been taken

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2、[单选题]Living in the central Australian desert has its problems,________ obtaining fresh water is not the least of which.

• A、for which
• B、to which
• C、of which
• D、in which

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3、[单选题]Government cannot operate effectively ________ it is free from such interference.

• A、so long as
• B、so that
• C、unless
• D、because

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4、[单选题]They usually have less money at the end of the month than ________ money at the beginning.

• A、which is
• B、which was
• C、they have
• D、it is

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5、[单选题]Language is a city ________ every human being brought a stone to the building of the city.

• A、which
• B、that
• C、it
• D、this

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