一道考古题请教,谢谢

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 proved easier.

(B) that is similar to artificial vision but one that has proved easier to solve

(C) similar to that of artificial vision but it has proved easier to solve

(D) similar to that of artificial vision, but the solution has proved easier

(E) similar to that of artificial vision but one that has proved easier to solve

answer: E,,,,why not D 求教

if D then "...to 'see' forms,but the solution has proved easier "