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In the near future, researchers _______ more space stations.

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What _______ when I called?

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I completely forgot about this. Give me a moment, I (do) _______ it now.

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I promise that I (not/ come) _______ late.

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Alice _______ the accident when she was catching the bus.

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The _______ can fall below zero degrees Celsius in winter.

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The prerequisite condition for a/an _______ planet is water supplies, appropriate temperatures and breathable air.

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The scientists believe that there might be some planets to _______ human life.