If there is always a 4-for-1 tradeoff between producing good X and good Y, it follows that the opportunity cost of X (in terms of Y) ____________________ and the PPF for these two goods is ______________________.

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decreases at low levels of X; a straight line

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rises at high levels of Y; bowed-outward

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decreases at high levels of X; bowed-outward

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is always the same; a straight line