a.Now back to the BLS chart, and to the prices of food and energy in the Consumer Price Index. Think about the global markets that trade oil and those that trade grain (maize, wheat, rice, etc). Regardless of what actually happened in the past year, can you think in general of examples of supply (S) shocks that can affect the price of (i) oil and (ii) grain that are not related to the general strength (or weakness) of the US economy? List at least two examples (one for oil and one for grain markets). [1 line]

Chart 2. 12-month percent change in CPI for All Urban Consumers (CPI-U), not seasonally adjusted, Jan. 2020 - Jan. 2021 Percent change 2.5 2.0 1.5 * X * 1.0 0.5 0.0 Jan'20 Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Jan'21 X X X All items All items less food and energy