As teacher you are not only tough but unfair:
- you didn't track any score regarding the second ohm's law
- my rambling about point 3 was more to demonstrate is such a huge subject with so many implications that I hardly believe I could use a forum post to even just list them all: you should have allowed at least half point for admitting the subject is so vast
- I admit my answer at point 2 was incorrect, but I believe 9 out of 10 would have understood I meant to say "current flows more in the easiest path"... And that was quite clear in the context of the remaining part of the answer
Anyway, I'm now working on your answers: at least I got the reason behind the two diodes!
Regarding the high pass filter question, I knew you were creating a voltage divider to get a 2.5V reading point, but why isn't that an high pass filter as well? Because the AC is not swinging to negative?