sometime是副词，可与过去时或将来时连用，表示"(在过去)某个时候"或"(在将来)某个时候"。如： I saw him sometime in May.
some time多数情况下作名词短语，意为"一些时间;一些时候";它还可以作副词词组，用来表示一个未肯定的时刻，此时它可与sometime互换。如： I'll be away for some time.
sometimes是一个表示时间频率的副词，意为"有时候"。如：Sometimes I help my mother with the housework.
some times是"几次、几倍"之意。如：They have been there several times.
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