This page is part of my unofficial solutions manual to the GRE Paper Practice Book (2e), a free resource available on the ETS website. They publish the questions; I explain the answers. If you haven’t worked through the Practice Book, give Section 3 a shot before reading this!

3.2: “Most spacecraft…”

The first clause describes an orbital environment that presents little risk to spacecraft. For our blank, then, we might say that the environment is becoming less safe or less low-risk. (Remember, when pre-filling blanks, aim for accuracy, not elegance.) The closest match for safe is benign (E), in the sense of “not harmful.” Crowded (A) and polluted (D) are the opposite of what we want. Invulnerable (B) and protected (C) might seem like attractive options; these words would aptly describe the spacecraft, but not the environment.

Vocab Notes

Most people have encountered the word benign in the context of medicine. When describing an illness or tumor, benign means “not seriously harmful” and is the opposite of malignant. But this is a specialized meaning. In general, benign has a stronger positive connotation; it means “gentle and kind.” So, for example, someone who “exerts a benign influence” is doing something good, and not merely refraining from doing harm.