There are two ways to delete a question:
1. Put your mouse on the question, and click on the [Delete] button appears.
2. Find the question in tree-form panel and click on it. Then click on [Delete] button on the top of the panel to delete it.
When you use tree-form panel to delete a question, there won't be any alert. So make sure it's the right question before clicking on [Delete]. Deleted question CANNOT be restored