more than/than/whereby

[fabxx]

This question is on the SAT OG book page 661 # 28

[In] the United States, the industrial [use of] plastics [is] greater [than steel], aluminum, and copper combined. [no error]

Why is [than steel] wrong? Isn't than used to compare the industrial use among plastics, steel, aluminum and copper?

<Second question removed.>

 

[xqby]

You would need a more complex linking phrase than just "than," to make it clear that the use is greater. Even just something like:
"In the United States, the industrial use of plastics is greater than that of steel, aluminum, and copper combined."

 

[fabxx]

Thank you!!