The first thing to notice is that this is a parallelism question. They throw in the word "tilting", which could mislead you into thinking that "changing...varying" would be parallel, but another phrase in the sequence -- "fluctuations and other deformations" -- makes it clear that we need a noun to maintain parallelism. Therefore, A, B and C are out. This is a good example of why you need to gather all the clues you can to determine what is parallel to what, rather than grab one clue and run with it.

D is better than E in terms of meaning -- the issue at hand is changes in the strain, not changes in the measurement, for one thing. Second, "variations in" is better than "variation among", because the geologists are looking for variations in (i.e. of) the electrical properties, which is expressed perfectly by the standard phrase "variations in." "Variation among" is not as clear here because it's singular (as if they're looking for a single abstract property of variation) and because "variations among" is usually used to describe populations or groups within which one is looking for variations -- as in "variations among bacteria" -- rather than the actual properties that one is examining for variations.