GMAT Sentence Correction (SC) | As virtually all the nation's 50 busiest airports are

Hi sanghar, this would not be logical. The sentence is talking about something in thepast (before jet planes weighing 800,000 pounds needed over two miles of runway). Hence,are built would not be the correct tense. We need to usepast tense here.

No. This issimple present andsimple past construct (1st clause and 2nd clause respectively).
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