Good question which I think you have made overly complex. I am an Avionics engineer and occasionally was roped in to teach the new pilots to our airline about aircraft systems. Unfortunately they simplify things a bit for the pilot course to the point where a smart pilot would figure out things didn't quite make sense which is where I came in.
Without looking to hard at your diagrams or multichoice questions I will just say this.
A synchronization bus usually is a simple wire running between the voltage regulators to make them share the load and stay in phase.
A bus tie connects the appropriate busses together to supply aircraft system loads.
If the voltage regulator cannot control the generator its connected to within limits it prevents the generator from coming online, being connected to the buss and tied to others.
On the machines I worked on the fault would read, " gen light wont go out, bus tie wont work", no circuit breakers opened and the mel was invoked.
Good luck and remember the diagrams they are feeding you are simplified, often they don't make sense if you look real hard at them. Try the Maintenance manual for the true story
