<span>D. There is no single topic sentence.
This paragraph is not focused under one single topic sentence, it moves throughout the features of the earth and how they interact and change the face of the planet. In order to bring this paragraph together more clearly, a topic sentence would have to be added that covers all the information in the paragraph.</span>
Can you explain your question more ?
In fiction, you would like to give variety to your word choices. In formal business or academic writing, You want to prevent ambiguity and so may use the same word again and again to make your meaning clear. For example "contract" might be used repeatedly rather than along with some synonyms for it.
