3. [4 pts] The following graph shows the annual average cost of regular retail gasoline in the US (the red line) along with the annual quantity of gasoline purchased in the US (the blue line), from 2000 to 2021. (If you want to play with the data yourself, there's an interactive version available here:https://fred.stlouisfed.org/graph/?g=TtRnLinks to an external site..)

Notice that during most of this timeframe the lines move in opposite directions. I.e., the price of gas fell and the quantity of gas purchased rose. (Or vice versa.) This would align with our "law of demand".

However, there are a few other periods (e.g., from 2002 to 2004, from 2017 to 2018, and from 2019 to 2021) when the lines move in thesamedirection. This means that the price of gas rose and the quantity purchased also rose. (Or they both fell.) This would seem to contradict our "law of demand".

But economists still believe the "law of demand" is valid. So, how might you explain the fact that we sometimes see gas prices and quantities moving in thesamedirection? (Briefly explain. Note: You don't need to give a specific explanation for each individual year. We're looking for a general explanation about why this may happen.)