For each input key-value pair, mappers can emit:
A.
One intermediate key value pair, of a different type.
B.
One intermediate key value pair, but of the same type.
C.
As many intermediate key-value pairs as desired, but they cannot be of the same type as the
input key-value pair.
D.
As many intermediate key value pairs as desired, as long as all the keys have the same type
and all the values have the same type.
E.
As many intermediate key-value pairs as desired. There are no restrictions on the types of
those key-value pairs (i.e., they can be heterogeneous).
Explanation:
Mapper maps input key/value pairs to a set of intermediate key/value pairs.
Maps are the individual tasks that transform input records into intermediate records. The
transformed intermediate records do not need to be of the same type as the input records. A
giveninput pair may map to zero or many output pairs.
Reference: Hadoop Map-Reduce Tutorial