1.price and quantity demanded The law of demand states that there is a negative relationship between price and quantity demanded. 2.pens and pencils Pens and pencils are the best examples of substitutes because they can be consumed in place of each other. The other examples are complements because they are typically consumed together. 3.a rightward movement along the demand curve. 4.price and quantity demanded 5.An increase in the price of sugar, an input. An increase in the cost of an input causes a decrease in the supply of cereal. The other options all cause an increase in the supply of cereal.