Have you ever worked at check out before? 这里的ever 和 before在...答:2、现在完成时往往同表示不确定的过去时间状语连用,如already, yet, just, before, recently,still, lately等。We have seen that film before. 我们之前看过那个电影。3、现在完成时常常与表示频度的时间状语连用,如often, sometimes, ever, never, twice, on several occasion等。Have you ever been...