Nancy hasn't begun working on her Ph.D.___________ working on her master's.

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In Australia, he made a lot of friends ___________English well to make himself ___________.

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Trees on the hills can stop rains from ___________away the soil.

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__________the rule you will take no difficulty to grasp the meaning of it.

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The soil __________down into the rivers when it rains.

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Would you please __________the little plants __________soil?

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Not only the artificial hill (假山) but also the newly - built bridge ________ the stream ________ the park more beautiful.

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In the forest, you can see different birds ________ in the sky.

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The trip was difficult and dangerous. ________, we had a kind and experienced guide.

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I ________ until they have returned .

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