A topic sentence is basically the sentence in a paragraph tell the reader what the paragraph is about or summarizes the content of it. Most paragraphs are composed by a topic sentence and a set of supporting sentences which are the sentences that explain the topic sentence through details, examples, evidence or other statements. Additionally, most topic sentences are placed at the beginning of the paragraph as it introduces the topic, subject or idea the paragraph is about. Considering the previous ideas, the sentence that is the topic sentence in this paragraph is sentence one "Don’t think that online stores are impersonal" this can be concluded not only because this is the first sentence, but because this sentence is the one that summarizes the content of the paragraph, this also means the other sentences explain the way online stores personalized their services and therefore sentence 2,3 and 4 support the main idea of the paragraph or the topic sentence which is sentence 1.
