Any variable can have a specific 'length' and, indeed, it's a good idea for all variables to have some defined storage capacity.
So it would seem cpQuizInfoAnswerChoice can hold up to 12 characters? Considering it's meant to just hold the selected choice, which would seem to most commonly be A, or B, etc...that doesn't seem unreasonable.
So you have longer answers you want to store? What are you trying to acheive? Maybe there's a better or alternative approach...
Sorry, but that is not correct: I used cpQuizInfoAnswerChoice even for answers to Short Answer questions. But I suspect that you tried to insert this variable in a text caption, and that you didn't change the default length which is 15 characters.
I blogged about this variable recently: