The correct topic sentence is Option B. A topic sentence depicts the overall idea of the paragraph in brief and here Option B serves the purpose as the paragraph compares the lakes and oceans in various ways. Option A is incorrect as it introduces us to the paragraph but does not clearly mention the content in brief. Options C and D are incorrect as they only depict certain factors on which the lakes and oceans are compared and are a part of the paragraph but they do not suit the purpose of a topic sentence.