The occurrence that could cause the demand curve for cars in your city to shift to the left is:
a layoff of 500 workers at the city’s airport.
This event would likely reduce the overall income and purchasing power of those laid-off workers, leading to a decrease in the demand for cars, as fewer people would be able to afford to buy them.
The other options would either increase demand (more people moving in, rise in wages) or represent a temporary increase in demand (sale at the dealership).