1.作频度副词用法：放在be动词和助动词后面；行为动词前.
特殊用法：
1 sometimes可以放在句首、句中和句末
2 often 也可以放在句末
如：
Tom never went to see his wife.．(在行为动词之前)
Tom has never been to China.．（在第一个助动词后）
Tom is never late for school.（在系动词后）
属于这一类的副词还有often,sometimes,always,usually,already,nearly,almost等.
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2.作频度状语,一般都用于完成时.
1）i've never seen such a beautiful place.
2）this is the most beautiful place i've ever seen.