"when compared to" idioms

[NikaT505]

In GMAT sentence correction book, page 223, Manhattan states that idiom "when compared to" is incorrect. I am confused because Official Guide for GMAT 2016, in its answer to question #116 states that "when compared to" is correct and is in fact the right answer choice ("...Sales in November, even when compared with sales in previous Novembers...)". Could you please help on this. I would really appreciate your help.

[RonPurewal]

this has nothing to do with idioms.

if you write "when compared to", you have to actually MEAN "when compared to".

e.g.,
The African elephant is the world's largest land animal, but it looks very small when compared to a jet plane.
--> here, "when compared to" is absolutely correct, because it's what we actually MEAN.
i.e., an elephant is actually really big, but, WHEN we put it side-by-side with an airplane, it suddenly looks really small (and only AT THAT TIME).

[RonPurewal]

this is the wrong place for your question, by the way, so this thread will now be locked. this sort of thing should probably be posted in either the MPrep non-CAT verbal folder (since it's from the strategy guide) or else the general verbal folder.