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.
Found exclusively on the Galapagos Islands, marine iguanas are the only species of iguana to enter the water, where they seek out the algae that make up the bulk of its diet.（）
A. marine iguanas are the only species of iguana to enter the water, where they seek out the algae
B. the marine iguana, being the only species of iguana to enter the water, searches for the algae
C. the marine iguana is the only species of iguana to enter the water, where it searches for the algae
D. marine iguanas are the only iguana species entering the water, where it seeks out the algae
E. the marine iguana is the only iguana species to enter the water, where they search for the algae
，若
，求a的取值范围。
