Restorers say that....

[gmatwork]

Restorers say that if allowed to remove and replace the discolored layer of varnish on the Mona Lisa, the colors Leonardo da Vinci painted nearly five hundred years ago will once again shine through.
A. If
B. if it is
C. if they are
D. when
E. when it is

OA：C

GMAT Prep Pack 1

E - it does not have a referent; when placed.........
seems to modify colors, distorting the whole meaning

D - same problem

Can't decide between A and D??

B - it does not have an antecedent; no pronoun agreement for possible antecedents for 'it'

[tim]

this doesn't look like an IR question. please repost in the appropriate section..