GMAT Sentence Correction (SC) | Re: On Earth, among the surest indications of sunspot cycles are

Beginning the sentences (A, B, C) with 'On Earth' means that the writer is an alien.

In A. B. C. 'On Earth' is an adverbial phrase that modifies 'verb' or 'whole sentence'
In D. E. 'On Earth' is an prepositional phrase that modifies 'among the surest indications'

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