Predator X, the largest marine predator ever discovered, would have been feared both for its razor-sharp teeth, which boasted a bite over 13 times more powerful than an alligator’s, and for its imposing size.

A. more powerful than an alligator’s, and for its
B. as powerful as an alligator, and for its
C. more powerful as an alligator’s, and had an
D. as powerful as an alligator, and its
E. more powerful than an alligator’s, and having an

(A) The original sentence is correct as written. The sentence presents a comparison between the powerful bites of two different creatures, Predator X and the modern-day alligator. The original sentence makes it clear that it is the two creatures’ bites that are being compared, not the creatures themselves.

Choices (B) and (D) both confuse the meaning by replacing “alligator’s [bite is implied]” with “alligator.” You can’t compare Predator X’s bite with an alligator; you must compare it with an alligator’s bite.

The overarching structure of the sentence is “Predator X…would have been feared both for x and for y.” Since the elements x and y constitute a list of characteristics, they must be in parallel form. As written, these two noun phrases are parallel: “its razor-sharp teeth” and “its imposing size.” Choices (C) and (E) create parallelism errors in removing the possessive pronoun “its” from the noun phrase “its imposing size.”

(A) is the best choice.
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"over" means "more than", using both "over" and "more" is wordy.

In this sentence, the words "over" and "more" are not both being used to convey the same concept, therefore using both words is necessary. The two concepts are that Predator X's bite is more powerful than the alligator's and the actual factor by which the bite is more powerful. Because the factor is not exactly 13 (perhaps it's 13.5), the author says "over 13." By using "over 13" to convey "more than 13" the author avoids repeating the word "more" while still conveying both concepts.