When you move to the right (and down) along a strictly convex indifference curve, the marginal rate of substitution

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["decreases", "is constant", "increases", "first increases, then decreases", "first decreases, then increases", "first increases, then constant, then decreases", "first decreases, then constant, then increases", "weakly decreases (i.e. either decreases or stays the same)", "weakly increases (i.e. either increases or stays the same)"]