Each Group of Sentences Can Be Arranged and Written as a Paragraph

Each group of sentences can be arranged and written as a paragraph. Select the letter of the sentence that would be the best topic sentence.
-_____

A) As climate change dries up the moist environments they need, more frogs die out.
B) The disappearance of frogs around the world is a disturbing sign of ecological problems.
C) Because frogs eat mosquitoes and flies that carry serious diseases, those illnesses rise as frogs become extinct.
D) Because many other species eat frogs, their passing pushes those species toward extinction.