A.  Developers should design Map-Reduce jobs without reducers only if no reduce slots are available on the cluster.
B.  Developers should never design Map-Reduce jobs without reducers. An error will occur upon compile.
C.  There is a CPU intensive step that occurs between the map and reduce steps. Disabling the reduce step speeds up data processing.
D.  It is not possible to create a map-reduce job without at least one reduce step. A developer may decide to limit to one reducer for debugging purposes.

Answer: C