<em>A. True. If it is possible to pass a single horizontal line through more than one point on the function curve, then the function is not one-to-one (it fails the horizontal line test).</em>
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<em>B. True. Any given input must lead to exactly one output.</em>
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<em>C. False. The vertical line test is used to determine if a relation is a function or not.</em>
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<em>D. False. The domain of a sequence is the set of natural numbers {1, 2, 3, ...}</em>
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<em>In summary, the answers are A and B</em>
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