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4.4. In general, and in terms of short-run and long-run elasticities, why do short-run demand and supply curves look very different from their long-run counterparts? Explain and indicate which period is seen as short run and which as long run. 4.5. If two products are substitutes, what must the magnitude of the cross-price elasticity of demand be (i.e. negative, positive, zero or infinite)