What is the range of the function: {(1, 3); (3, 5); (5, 7); (7, 9)}?                                

    A. {1, 3, 5, 7}                                               

    B. {1, 9}                                               

   C. {3, 5, 7, 9}                 

    D. {1, 3, 5, 7, 9}