The part I didn't understand is: mid(list,random(len(list)),1)
In my case the list of variables will be something like this: acd
So to extract a random variable name (one letter) from that string I'm using mid() expression, which extracts one character at random(len(list)) position.
In your case I suggest a different approach. You can build a list of variables separated by space or comma:
apples pears oranges
Having space as a separator is easier because you can use trim(list) to remove any extra leading/ending spaces. Then extract one variable name using tokenat/tokencount:
Set list to trim(list)
Browser Log tokenat(list, random(tokencount(list, " "), " ")
See the documentation if you need help with any of these expressions:
construct.net/en/make-games/manuals/construct-3/plugin-reference/text