SAT writing question !!!

A(In) the United States, the industrial B(use of) plastics C(is) greater D(than steel), aluminum, and copper combined.
E(no error)

The answer is D and i couldn’t figure out why. Can anyone explain it to me? By the way, the parenthesis replaces the underline in the question.
This problem is from college Board practice test so i’ll say it’s pretty reliable.(not like those horrible Kaplan practice tests)

My guess would be because it’s not exactly clear what you’re comparing. You’re comparing the USE of plastics and the USE of steel, aluminum, and copper. Without that word, you’re not comparing apples to apples.

A more correct version might be, “…is greater than that of steel, aluminum, and copper combined.” As is, it could technically sound like you’re talking about all the steel, aluminum, and copper in the world. We don’t know what amount or context you’re referring to.

that actually makes a lot of sense! Thank you!!!

It’s about parallel structure, OP. Always look for the parallel structure – comparing the same categories. (Use of with use of, as bodangles explained. But the pronoun “that” also suffices, should that be an option.)