Proposition/opposition pieces allow the write to write both views of what is usually a controversial issue. The first half is usually written for argument A and the second portion is usually to argue point B. In the conclusion the writer expresses what viewpoint they take.
A descriptive piece should create a vivid image of a person, place or an idea. This form of writing relies more heavily on detail that draws on all of the senses. This enables the reader to tap into the writers sense.
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After talking with Chelsea, I decided I'll most likely write my research paper in the descriptive mode of writing