Let \({\rm{f}}\left( {\rm{x}} \right):\left\{ {\begin{array}{*{20}{c}} {{\rm{x}},{\rm{\;\;\;x\;\;is\;rational}}}\\ {0,{\rm{\;\;\;x\;is\;irrational}}} \end{array}} \right.\) and \({\rm{g}}\left( {\rm{x}} \right):{\rm{\;}}\left\{ {\begin{array}{*{20}{c}} {0,{\rm{\;\;\;x\;is\;rational}}}\\ {{\rm{x}},{\rm{\;\;\;x\;is\;irrational}}} \end{array}} \right.\)If f : R → R and g : R → R, then (f – g) is

• A. one-one and into
• B. neither one-one nor onto
• C. many-one and onto
• D. one-one and onto