"Has had" 是一个简单的现在完成时态，它表示某件事情从过去的某个时间点一直持续到现在。
比如：- She has had a headache all day. (她从早上开始就一直头痛。)"had had" 则是一个过去完成时态，它表示某件事情已经完成，发生在过去的某个时间点。比如：- By the time she got home, she had had dinner. (她到家的时候，已经吃过晚饭了。)另外，"had had" 也可以用来表达虚拟语气中的过去完成时态。比如：- If he had had enough money, he would have bought a car. (如果他有足够的钱，他就会买一辆车。)总的来说，区别在于 "has had"强调的是过去到现在的持续性，而"had had" 则是强调过去某个时间点的完成。
