题目：
The following questions present a sentence, part of which or all of which is underlined. Beneath the sentence, you will find five ways of phrasing the underlined part. The first of these repeats the original; the other four are different. If you think the original is best, choose the first answer; otherwise choose one of the others.
These questions test correctness and effectiveness of expression. In choosing your answer, follow the requirements of standard written English; that is, pay attention to grammar, choice of words, and sentence construction. Choose the answer that produces the most effective sentence; this answer should be clear and exact, without awkwardness, ambiguity, redundancy, or grammatical error.
No giant squid has ever survived in captivity because these giant animals of the deeps require extremely high water pressure for the purpose of maintaining its internal osmotic balance.（）
A. deeps require extremely high water pressure for the purpose of maintaining its
B. deep requires extremely high water pressure to maintain its
C. deep require extremely high water pressure in order to maintain their
D. deeps requires extremely high water pressure so that it can maintain its
E. deep require for maintenance extremely high water pressure for their
答案：
参考答案：C
解析：
A is incorrect because "for the purpose of maintaining" is unidiomatic and the singular "its" modifies the plural "animals." B incorrectly uses the singular "requires... to maintain its" when "animals" is the subject. D also incorrectly treats the subject as singular. In E, it is unclear what "maintenance" refers to. C is the best answer.
