Normal faulting is most often associated with mountain building along boundaries, whereas reverse faulting is generally observed at boundaries.

Normal fault is associated with downward boundaries. A downthrown block between two normal faults moving towards each-other is called a graben and an upthrown block between two normal faults moving away from each other is called a horst.  

The opposite of a normal fault is called a reverse fault and it is observed in upward boundaries.   

your answer would b. the missisipi river

hope i you : )