Someday computers may be able to "see" forms, just as they now can be made to recognize voices, a problem of perception that is similar to artificial vision, but the solution has prove easier.

A. that is similar to artifical vision, but the solution has proved easier
B. that is similar to artifical vision but one that has proved easier to solve
C. similar to that of artifical vision but is has proved easier to solve
D. similar to that of artifical vision, but the solution has proved easier
E. similar to that of artifical vision but one that has proved easier to solve.

IMO : D
OA is E