Sentence Correction

I found this problem on one of the old paper test, so there is no explanation. I incorrectly answered D and have a feeling my error partly involved tense, although I'm not sure the the exact rules as they apply here.

Any insight would be much appreciated.


Art historians are using a process known as infrared scanning in analyzing the Mona Lisa to determine if it has been altered since completion and if Leonardo da Vinci first sketched the figure in black, as done by many artists of the time.

(A) if it has been altered since completion and if Leonardo da Vinci first sketched the figure in black, as done

(B) if it had been altered since completion and if Leonardo da Vinci first sketched the figure in black, a practice employed

(C) whether it has been altered since completion and whether Leonardo da Vinci first sketched the figure in black, a practice employed

(D) whether it was altered since completion and whether Leonardo da Vinci first sketched the figure in black, as was done

(E) whether it had been altered since completion and whether Leonardo da Vinci first sketched the figure in black, a practice done