How to process Natural Language Question in order to find target variable?


I am building an intelligent QA bot which will answer user provided question. As of now, I have extracted the super-class and sub-class of the question by applying SVM but, unable to find the target variable in the question. For instance,

Question : How far is it from Denver to Aspen ?
here, Super-class = Numeric, Sub-class = distance, Target = Denver to Aspen

Please help with any approach to find target variable. Thank you!