If the marginal rate of transformation is constant throughout, the production Possibilities Frontier will be

Option 1 -> A concave PPF indicates increasing MRT, not constant.

Option 2 -> A convex PPF indicates increasing opportunity costs with varying MRT.

Option 3 -> A linear PPF has constant slope throughout, meaning constant MRT.

Option 4 -> PPF is always downward sloping due to trade-offs between goods.

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Hence, Option 3: Downward sloping and linear -> When the Marginal Rate of Transformation (MRT) is constant, the opportunity cost of producing one good in terms of another remains the same throughout. This constant slope results in a straight line (linear) PPF. The PPF is downward sloping because resources are scarce and producing more of one good requires sacrificing some amount of the other good. A linear PPF implies constant opportunity costs, which occurs when resources are perfectly substitutable between the production of two goods. -> correct