This post is closed by a moderator. I think the reason is that it starts to have too many answers which I didn't expect. How can I reopen this question? I want to convert it to Community wiki post but I don't have any option in the edit box.
I think the reason is that it starts to have too many answers which I didn't expect.
This isn't quite right. We decide whether to close a question on the merits of the question, not the answers. The problem with a question of the form What are examples of X? is that there are many possible answers, and so it naturally attracts many partial answers, instead of one or a few definitive answers. You can read some discussion on this type of post here and here.
As for reopening it, it's hard for me to see how you could edit the question to make it more focused without completely changing what you are asking.