I don't understand your last question, probably a terminology issue. Which variable are you talking about? Is it defined in the Captivate file, did it get a value?
I think I understand what Adam means. The correct answer is going to be the value of a variable, which might change on the fly.
By default, a Captivate TEB that is set to validate can only validate against the correct answers entered into the validation list. If you want to validate against a variable, but you don't know how to hack the JavaScript behind the Captivate published output, then you'd have to turn off the TEB's normal validation, remove the TEB's own Submit button, add a Smart Shape button to trigger a Conditional Advanced Action to perform the Validation of the TEB's associated variable against the current value of this other variable you speak of.
Setting this up is not that difficult, but if you're a rank beginner in Captivate it might be somewhat over your head.