Answer:
The thunderstorm that destroyed Midland Farm's summer crop of corn would be considered an external shock, which is a type of exogenous variable in economics. An external shock is an unexpected event that occurs outside of a business or economic system that affects its performance, and is beyond the control of the individuals or firms affected by it. In this case, the thunderstorm is an external shock that has had a negative impact on Midland Farm's profits by destroying their crop, which is an important input for their production process.