1 . This is why the focus now is on ________ (sustain) development.(所给词的适当形式填空)
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2 . Try to buy wood that you know has come from a ________ (sustain) source. (用所给词的适当形式填空)
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3 . Cultural tourism is an effective way for________ (sustain) development of tourism. (所给词的适当形式填空)
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