26. 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

【正确答案】 A

【答案解析】 Parallelism; Rhetorical Construction; Grammatical Construction
This sentence about the essential role oceans play in maintaining conditions for human existence on land begins with a participial phrase describing the vastness of the oceans, followed by the main clause (oceans play an essential role...). The object, role, is modified by a prepositional phrase that indicates what kind of role the oceans play (it plays a role in maintaining the conditions for human existence on land). This statement about the ocean's role in maintaining terrestrial conditions is elucidated by two parallel participial phrases that describe the oceans, explaining how they maintain conditions essential for human existence on land (moderating... and giving...).
A Correct. This version of the sentence effectively conveys the means by which the ocean plays an essential role in maintaining the conditions for human existence on land, using parallel verb forms.
B This version of the sentence is ungrammatical; and giving... suggests that this is part of a series of participial phrases, but it is not.
C The conjunction followed by a prepositional phrase and by moderating... anticipates a new subject—an agent that does something by moderating—but this subject never appears.
D This version of the sentence is structured as a series of verbs—cover, play, and moderate—all describing things the oceans do; the final participial phrase giving... water... violates the parallel structure set up in the sentence.
E This version of the sentence correctly makes playing an essential role... a function of the oceans' coverage of Earth's surface, but the introduction of a new main verb moderate fails to indicate that what follows (moderating temperature and returning pure water) identifies the role oceans play in maintaining conditions for human existence on land. Furthermore, the participial phrase and giving pure water... violates the parallel structure set up by the series of main verbs that appear earlier in this version of the sentence.
The correct answer is A.