Explanation

Creating a filter: supposing that we can't find an error or create a filter, we go straight to the answer choices.

Finding objective defects: in choice (B), the words "and have" at the end makes the sentence ungrammatical. The phrase "and have" appears to refer to the team of researchers as its subject, but there is no previous verb to require the word "and." We can see this more easily to see once we ignore the modifying phrase starting with "having spent"; the word "and" is without purpose. Choice (C) has the same program as (B). Choice (D) also creates a non-sentence, leaving the verb "discovered" without a subject. Choice (E) has the same problem as (D). The correct answer is (A).