never presented means not at all, and implies once, as I understand
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送交者: conner 于 2011-08-10, 14:35:10:
回答: never presented和have never presented也都可以 由 方舟子 于 2011-08-10, 12:01:45:
have never presented implies one or more times. The reference have appeared more than once. I think have .. is better.
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