The statement that best explains how a major event could impact grain, a primary commodity, is:
"A hurricane destroys grain fields across the Midwest of the United States. Due to the hurricane, the quantity of grain decreases and the price increases."
This scenario illustrates how a significant adverse event (such as a hurricane) can reduce the supply of a commodity (grain), leading to a decrease in quantity available in the market, which typically results in an increase in price due to supply and demand dynamics.