I have release the range and sheet like this:
　　　　　　　　// Release dispatch pointers.
range.ReleaseDispatch();
sheet.ReleaseDispatch();

book.Close( covTrue, covOptional, covOptional );
app.Quit();

1. Is this not enough? What should I add?
2. "You might also need to destroy your "app" reference after doing app.Quit "
How to do this? I think I haven't done the destroy step because I don't
know how and everybody just use the Quit().

Thank you.