# Covering 71 percent of Earth’s surface, the oceans play an essential role in maintaining the conditions for human existence on land, moderating temperature by the absorption of heat and carbon dioxide, and giving pure water back to the atmosphere through evaporation.

Covering 71 percent of Earth’s surface, the oceans play an essential role in maintaining the conditions for human existence on land, moderating temperature by the absorption of heat and carbon dioxide, and giving pure water back to the atmosphere through evaporation.

A. Covering 71 percent of Earth’s surface, the oceans play an essential role in maintaining the conditions for human existence on land, moderating

B. Covering 71 percent of Earth’s surface and playing an essential role in maintaining the conditions for human existence on land, the oceans moderate

C. The oceans cover 71 percent of Earth’s surface and play an essential role in maintaining conditions for human existence on land, and by moderating

D. The oceans cover 71 percent of Earth’s surface, play an essential role in maintaining the conditions for human existence on land, and moderate

E. The oceans cover 71 percent of Earth’s surface, playing an essential role in maintaining the conditions for human existence on land, and they moderate

Correct Answer Below (so you don’t see it while reviewing the question)

## In Depth Explanation: Covering 71 percent of Earth’s surface…

Here’s a modifier question with some list parallelism thrown in for good measure. Some of the choices create a list in the beginning while the correct one is structured as modifier.

Consider the overall flow of the sentence. Is it a whole bunch of somewhat similar level facts about the oceans or is there a hierarchy? I’d say the latter. Because…

You’ve got this big idea: the oceans play an essential role in maintaining the conditions for human existence on land

And then you have some details expanding on that idea.

Getting a sense for the flow of the sentence will help you evaluate what type of structures are appropriate.

The list is probably the best place to start but let’s start at the end of the sentence.

Because part of the list is fixed, “…and giving”, let’s match that.  So the first item in the list must be parallel with “giving”. Any choice that doesn’t have “moderating” is out. That eliminates most of the options.

Many people over-focus on the underlined portion of the sentence but there are treasures to be found elsewhere. And sometimes the fixed portion of the sentence is incredibly helpful because it must be matched.

Covering 71 percent of Earth’s surface, the oceans play an essential role in maintaining the conditions for human existence on land, moderating temperature by the absorption of heat and carbon dioxide, and giving pure water back to the atmosphere through evaporation.

(A) Covering 71 percent of Earth’s surface, the oceans play an essential role in maintaining the conditions for human existence on land, moderating

The leading modifier checks out as does the list, moderating and giving.

(B) Covering 71 percent of Earth’s surface and playing an essential role in maintaining the conditions for human existence on land, the oceans moderate

Missing a main verb. Not a complete sentence. Also missing parallelism with “and giving”.

(C) The oceans cover 71 percent of Earth’s surface and play an essential role in maintaining conditions for human existence on land, and by moderating

“And by moderating…” is set up as an independent clause joined by a conjunction. It needs to stand on its own. Does it?
(D) The oceans cover 71 percent of Earth’s surface, play an essential role in maintaining the conditions for human existence on land, and moderate

The first list seems parallel but how does ” and giving” factor in? Similar to C it looks like it’s now set up as an independent clause but doesn’t work because it isn’t a complete sentence. Clearly it’s intended to be a part of a list.

(E) The oceans cover 71 percent of Earth’s surface, playing an essential role in maintaining the conditions for human existence on land, and they moderate

Not parallel. The oceans cover, playing, and they moderate.  Also missing parallelism at the end with “and giving”. It has the same problem that “and giving…” is now set up as independent close but isn’t a complete sentence.