Where do you increment the variable “CurrentQuestionIndex”?
Since you made array
Then you need another variable
Call it RNG or something
You set RNG var to RandomInRange(0,VariableChildCount(ArrayVariable)-1)
Now you change text to ArrayVariable[RNG]
Where you also delete child in ArrayVariable at index RNG
The existing variable CurrentQuestionIndex can be used for that.
Yes but as you see either some screenshots are missing here or he is missing some events
That is why i prefer to explain to him whole logic
Instead of patching my idea with what we see here
I understand your logic, but how to write the event, i am so confused 
Going from top to bottom
1 - 1st you are rolling random number for RNG variable
Since you always want it minimum number to be 0 it will be always 0 there
As max number you just put variable child count of array variable - 1
Cause if you have 7 child vars then it means 1st start from 0 and last will be 6
For example
How many variables are there
1 2 3 4 5 6 7
0 1 2 3 4 5 6
Their index numbers
So even so you have 7 child vars index of last one is 6th cause 1st child starts with index 0
2 - You are changing text objects text to one of your child vars from Array rolled by RNG var
3 - You remove child by its index that was rolled by RNG var
This is only reason you need RNG var cause you need to keep track what was rolled
Since whole event runs on trigger once
Once you press space text will change once
But even so child variable was already removed text WON’T change
Only downside to this method is that until you press space for the 1st time
Text will display nothing
But you could set it at beginning of scene to "“Do something to roll question”