GMAT Sentence Correction (SC) | Re: Art historians are using a process known as infrared

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