在过去几十年里，人们对其在外语教学领域的认识几经反复。

Within the last few decades, its importance in foreign language learning has been reassessed several times.

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临清坳陷东部第三系油气勘探几经反复，属低勘探程度的老区。

After exploration over and over again, the eastern part of Linqing depression in Tertiary became an old area with low exploration degree.

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