A.  The distributed cache is special component on namenode that will cache frequently used data for faster client response. It is used during reduce step.
B.  The distributed cache is special component on datanode that will cache frequently used data for faster client response. It is used during map step.
C.  The distributed cache is a component that caches java objects.
D.  The distributed cache is a component that allows developers to deploy jars for Map-Reduce processing.

Answer: D