A and C
What type of scarf joint do you believe is the most probable?
Some types of scarf joints need removing of rather large areas of original materials to be proven effective and as strong as the original type. From the side they would look like very sharp dart-like objects, one on top of the other, a bit similar as in crippen's post.
Other scarf joints are more like "step" joints (sorry, non-native English writer here..) where the "steps" can be subject to stress and creep but this saves on material.
One of the most material effective scarf joints is where you cover a piece of the original material with the repair (whilst doing this "step" joint - sorry for not knowing the proper name!), this would lead to a "bump" and may affect aerodynamics. My guess is that something like this is what happened to ATC Watcher's glideplane.