Explanation

Creating a filter: When we read the prompt, we can imagine it to be without the appositive phrase, "specifically gravitational effects," and the prepositional phrase before the comma all the way back to "in the universe," since such phrases can be removed without altering the grammar around it. That gives us, "the seeming absence... believed to be." We are missing a verb, an "is."

Applying the filter: our expectation is present in answer choice (B). Note that choices (C) through (E) all set up a proper subject-verb pair for the latter clause of the sentence, but they leave the original subject "absence" without a verb. The correct answer is (B).