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Answer (C) is correct . Purchasing from parties related to buyers or other company officials is a risk factor because it suggests the possibility of fraud. Such conflicts of interest may result in transactions unfavorable to the company.

Answer (A) is incorrect because The requesting department normally develops specifications.
Answer (B) is incorrect because Open purchase orders are customary for high-use items.
Answer (D) is incorrect because An approved vendor list is often maintained as a control factor to help ensure that purchases are made only from reliable vendors. However, rotation is not usually appropriate.