Every time you require input from the user, a grammar specifying the valid utterances for that interaction must be identified.

每次您要求用户输入时，必须标出为该次交互规定有效话语的语法。

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Additionally, many Web sites do not want to maintain, or require users to continually provide, the same profile-related information just to ensure that the user credentials are valid.

另外，许多Web站点不愿意自行维护用户个人信息，也不愿意要求用户提供这些信息。

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