What is the final step in how people process messages they receive? a. processing information together with prior knowledge b. applying and testing for confirmation c. paying attention d. arriving at conclusions and understanding

This process is actually consists of all the options represented above, I put them in correct order. 
1) C. paying attention. This is the very first action that is needed to focus for understanding.
2) A. processing information together with prior knowledge. At this stage the analysis is started through comparing your personal experience with the new one.
3) B. applying and testing for confirmation. You have just made an analysis of the information and you begin to check whether it is reasonable and sensible.
4) D. arriving at conclusions and understanding. The answer you are looking for. The last stage that leads you to complete understanding of information and you can easily estimate its importance.