Candice needs a topic sentence for the third paragraph (sentences 19–21). Which of the following sentences should be inserted before sentence 19 to introduce the ideas in this paragraph?
A) Over time, a vast array of creatures has come to inhabit the Great Barrier Reef.
B) Marine animal species that are threatened are protected by the Great Barrier Reef Marine Park Authority.
C) The biodiversity of the Great Barrier Reef ensures its long-term existence.
D) The waters along the Great Barrier Reef provide a habitat for marine animals that researchers study.