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Tracy: “I think plastic bags are not as harmful as people say. Instead, they provide great convenience.”

Nathan: “______. Plastic bags are among the biggest threats to our environment.”

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Natural resource managers ______ the needs and behaviors of wildlife.

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The national park was established to ______ the ecosystem of the limestone forests.

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Ha Long Bay is the product of geological ______ that lasted more than 500 million years.

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The ______ living by the river has been uprooted and then transported away.

The new varieties of rice grow well ______ in poor soil.

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The search for the new kind of penguin in Antarctica has been ______ international media attention.

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Scientists have been studying different ecologies ______ the 20^th century.