Read the Original Sentence Carefully, Looking for Errors:
Although this sentence, as written is not grammatically incorrect, it is wordy and awkward. In particular, the passive "there is ..." construction is weak, and the separation of "three" from "or more" at the end reduces readability. Check the choices for a clearer, more concise version.
Scan and Group the Answer Choices:
There is no useful split among the choices, so review each choice and eliminate ruthlessly.
Eliminate Wrong Answer Choices:
Eliminate (B). "Unless there be no absence of ..." is even more wordy and awkward than the original. A more streamlined way say "unless there be no absence of corroborating evidence" would be unless there is corroborating evidence or, even better, without corroborating evidence.
Eliminate (D). "Should there not be ..." is as awkward as the original. Also, the original sentence speaks of the presence or absence of evidence, while this sentence talks about corroboration being "in evidence," or apparent. This change of wording subtly distorts the sentence's meaning.
Eliminate (E). "With evident corroboration ... being absent" as awkward as the original. The word "being" is rarely correct in GMAT Sentence Correction.
(C) conveys the same meaning as the original but much more directly and clearly, and this choice is correct.