Hadoop Streaming Uses the Standard Input and Standard Output Streams

Hadoop streaming uses the standard input and standard output streams as follows:

A) Hadoop supplies the input to the mapping script-called the mapper. This script reads its input from the standard input stream. The mapper writes its results to the standard output stream.
B) Hadoop supplies the mapper's output as the input to the reduction script-called the reducer-which reads from the standard input stream.
C) The reducer writes its results to the standard output stream. Hadoop writes the reducer's output to the Hadoop file system (HDFS) .
D) All of the above statements are true.