I'm so sorry, but it is not possible to learn the modified and unmodified envelope from here. Because this subject is very difficult for every person who is learning French. So you can learn this subject only by attending a French course or by living in a country which is native french. But if there is anything needed for your homework on this topic, I can help.If you want, I can say a few sentences about this subject as an example, but as I said, unfortunately you can't understand from here.
But if you want to learn French, don't give up like the others;))
If any other question i can help:)
