现在完成时，由助动词 have/has 和过去分词构成，不仅表示过去对现在的影响，也用于强调次数。在强调次数时，常用词汇如 already, yet, just, ever, never, before, twice, three times 等置于 have/has 之后，以明确表达动作发生的次数和频率。掌握这种用法对英语学习者来说非常重要。
强调次数时，我们通常会使用副词如 already, yet, just, ever, never, before, 或者表示次数的词汇如 twice, three times, 等等。这些词汇通常会放在助动词 have/has 之后，形成现在完成时的强调形式。
例如：
- I have already eaten breakfast twice this morning. (我今天早上已经吃了两次早餐)
- He has just finished his third book this month. (他本月已经读完了第三本书)
- Have you ever traveled to Europe before? (你以前去过欧洲吗？)
- She has never been to a concert before. (她以前从未去过音乐会)
