Grocery...!!!

i received a pm.

the GMAT doesn't test punctuation, so i don't want to extend this discussion about commas -- it's a waste of all of your time.
the only time you should care about punctuation is when it actually creates a different construction. for instance, a "comma + ing" modifier is fundamentally different from a "no comma + ing" modifier.

the problem with (f) is "carrying"; this would be wrong.
NO COMMA -ING modifiers imply that something is happening in the same timeframe as the action to which it's attached. therefore, "carrying" would (absurdly) imply that the duct was already carrying waste heat as the owner was installing it.

if you write (f) with "to carry" instead of "carrying" (and preferably with no commas, although you shouldn't care about that), then it is fine.
it has a slightly different meaning -- it suggests that the fans and the duct are somehow related (hence why you're grouping them), but that they are not related to the air compressors in the same way.