The correct option is this: WRITING IS DIFFICULT BECAUSE SO MANY SKILLS ARE INVOLVED. A topic sentence refers to the sentence which expresses the main idea of the paragraph in which it occurs. The topic sentence is usually the opening sentence in the paragraph; the other sentences in the paragraph just serve to support the topic sentence.
<span>Out of Tammany Hall, Boss Tweed ran perhaps what was the most corrupt and most powerful New York City machine. He was accused of his corruption operations that were revealed in New York Times.</span>
