Sure, you have different options for separation.
For example tag each question. (a new field for each line)
You could use a different z-index for different text files/subjects. (I think I would prefer that one)
You could use more than one array, one for each subject.
You could use one text file and use another separator to divide subjects and you'll save the info somewhere which x-index-range contains which subject.
Ofc depending on the way you separate the questions in your array(s), you must modify the algorithm that shows the questions.
You can also add a tag to questions for their difficulty level.
So a text file could look like this;
Question 1?;right answer;wrong answer 1;wrong answer 2; wrong answer 3;1
Question 2?;right answer;wrong answer 1;wrong answer 2; wrong answer 3;2
Question 3?;right answer;wrong answer 1;wrong answer 2; wrong answer 3;2
Question 4?;right answer;wrong answer 1;wrong answer 2; wrong answer 3;3
1 would be easiest, 2 easy, 3 normal, and so on...
And then let the game increase the difficulty over time.