Why is the answer d? 'war brewing', 'communication age beginning' are gerunds but 'the industrial age well established' is not a gerund.

Jennifer, this practice set is about faulty parallelism, so we want to select a pattern that has: noun, noun, noun; or verb, verb, verb.

In this case, the parallel is established by "war brewing in Europe", which is a noun followed by an explanatory clause. Then, "the industrial revolution well-established" is also a noun followed by a clause. But, "a nascent communication age" is a noun with an adjective before it, hence they are not parallel.

The answer d corrects this, with "the communication age beginning", which is another noun followed by a clause. It doesn't matter whether the explanatory clause is gerund or not.

Isn't the second phrase about industrial revolution not in parallel