Question

Have you had your lunch yet? 你吃午饭了吗？为什么have要变成had

Answer 1

答案是：had 在这里是 have 的过去分词，现在完成时的构成是：have/has +过去分词

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Answer 2

句子是[现在完成时] have/ has + 动词[分词式](had)
I have had my lunch already.
Has she done her home work yet?
She has done her home work.

Answer 3

这是 现在 完成时，had是have的过去分词,