Geologists believe that the warning signs for a major earthquake may include sudden fluctuations in local seismic activity, tilting and other deformations of the Earth’s crust, changing the measured stain across a fault zone, and varying the electrical properties of underground rocks.
(A) changing the measured strain across a fault zone, and varying
(B) changing measurements of the strain across a fault zone, and varying
(C) changing the strain as measured across a fault zone, and variations of
(D) changes in the measured strain across a fault zone, and variations in
(E) changes in measurements of the strain across a fault zone, and variations among
As per OG, in the original sentence changing and varying are used as verbs rather than nouns. I dont understand how that is true because an ing form needs to be preceded by a 'to be' verb to qualify as a verb. Am I missing something? Could someone please correct me. Thanks!
I'd pick D. For a better explanation, you may want to look at this:http://www.urch.com/forums/gmat-sentence-correction/97221-geologists-believe.html