studetns attempted successfully,but from 2 days ago i lost one question ,i see 29 questions in the quiz,and the mark of the attempted students has changed.
Someone must have deleted the question. The logs may tell you who.
Probably you can fix things if you can re-create exactly the same question with exactly the same question id in the database. You will only be able to do this by fiddling around in the database. This is not the sort of thing you should do on your live site, so make a backup copy and practice on the copy first to make sure you know what you are doing. Good luck.