I had not learned of Super User community until two days ago when my question was migrated from Software community to Super User community. (I did not remember that I had joined in this community 10 months ago, I am very sorry.)
Ok then, I am so surprised that people here are nice and trying their best to help. But I found that whenever I tried to post a new question here, I would be requested to log in again before I could post it. It was strange to me since I had already logged in to Stack Exchange community.
I have no idea why this happened.