Enthuware

I don't understand why option three (It may print any combination except: a, or b, or a, b, or b, a) is the correct answer! Here is my understanding:
I know that thread execution is controller by the OS scheduler and it's impossible to guess the order of code execution of two independent threads. With that being said, option one (It may print any combination of the keys) is the correct answer because there is a possibility that the scheduler might want to execute all the code in the second thread before starting the first one.

Yes, that is a possibility and the output generated in that case is covered in option 3.

I also agree that the the first option should be correct and not just the third. Plus I seriously doubt that such ambiguity is presented in the actual exam (? hopefully)

As mentioned above, the third option includes the case given in the first option. So, if you have to select 1 option, then option 3 is the best option.

I would call this question and answer to this Super Tough!
For a non english speaking it is a bit harder to understand.