A.  Hadoop API will convert the data to the type that is needed by the reducer.
B.  Data input/output inconsistency cannot occur. A preliminary validation check is executed prior to the full execution of the job to ensure there is consistency.
C.  The java compiler will report an error during compilation but the job will complete with exceptions.
D.  A real-time exception will be thrown and map-reduce job will fail.

Answer: D