A.  The default input format is xml. Developer can specify other input formats as appropriate if xml is not the correct input.
B.  There is no default input format. The input format always should be specified.
C.  The default input format is a sequence file format. The data needs to be preprocessed before using the default input format.
D.  The default input format is TextInputFormat with byte offset as a key and entire line as a value.

Answer: D