Pairing Up

First things first. We use the Pairing Strategy to identify any synonym pairs among the six answer choices. There are usually two, sometimes one, sometimes three. We call the "triple pair" the Great White Buffalo.

Pair 1: comprehensive/inclusive
Pair 2: universal/ubiquitous
Maybe Pair: fundamental/significant
- They're not REALLY a pair but they can both mean "important."

The Right Answer

Use Math Strategy here. The phrases "and" and "almost as" indicate that the two ideas support each other. The first states that RNA is "common to all living beings." To maintain that idea, we guess a word like "common" or "widespread" for the blank.

The best match for this guess is the pair universal/ubiquitous.

The Wrong Answers

comprehensive/inclusive: We have no evidence whether RNA or DNA includes anything.
fundamental/significant: Setting aside the fact these two are not REALLY a pair, we have no evidence that RNA and DNA are important. I mean clearly they are. But the sentence does not explicitly mention their importance.