Option C: Decrease in AD

Deflation, the opposite of inflation, refers to a situation where an economy experiences a general reduction in the price levels of goods and services. While inflation reduces a currency's purchasing power, deflation increases it.

Recessions, on the other hand, are characterized by reduced economic activities over a period in a designated area.

Simultaneous recessions and deflations can occur when an economy's aggregate demand decreases to a level that affects real GDP and price levels respectively. With this in mind, successive deflation and recessions can be best explained by a decrease in an economy's aggregate demand. Option C is, therefore, the correct choice.