Video Explanation

Text Explanation

A question about the energy-intensive Hall-Héroult process for extracting aluminum metal from its ore.     

Split #1: Missing verb

The gerund phrase beginning with “extracting” is the subject of the sentence.  This subject needs a verb. Choices (A) & (B) commit the famous missing verb mistake: they have, respectively, a participle and an infinitive where they need a full verb.  These choices are incorrect.

Choices (C) & (D) & (E) have full verbs, so they do not commit the mistake.  Choice (C) illogically use the present progressive “is making,” so this choice is incorrect because of verb tense.  

Split #2: Where

On the GMAT, in the formal language of Sentence Correction, the word “where” has to refer to a physical location.  

“... China, where most of the characters have remained unchanged since the time of Confucius.”

“... the surface of Venus, where it rains sulfuric acid.”

“... New Windsor, NY, where Washington refused the crown.”  

These are all physical locations: one of the world’s oldest civilizations, the surface of a nearby planet, and Mike’s hometown.  

In colloquial American English, folks use “where” in all kinds of metaphorical ways.  

“... the point in a conversation where …”

“... the Symposium, where Plato says …”

“... the Trout Quintet, where a double-bass plays …”

Those are not physical locations.  On the GMAT, these uses of “where” would be incorrect.  

Similarly, the Hall-Héroult process is not a physical place, so “where” is illegal.  Choices (A) & (E) make this mistake and are incorrect.

The only possible choice is (D).