Here's the consensus view on the origins of our Gospels:
The problem solved is stated here, our Mark did first of all appear. For Luke and Matthew used him both, but Luke and Matthew, nothing loath, to add some more used "Q" for "Quelle," and special sources "M" and "L."
Make sense? Not to me. I'll be blogging about this topic this coming week and challenging the scholarly guild. I hope you'll join me.