Option 1 -> Fall in private consumption (C) directly reduces one component of AD, causing AD to fall.
Option 2 -> Fall in exports (X) reduces net exports (X-M), leading to a fall in AD.
Option 3 -> Fall in imports (M) increases net exports (X-M) since imports are subtracted in AD formula, causing AD to rise, not fall.
Option 4 -> Fall in government expenditure (G) directly reduces one component of AD, causing AD to fall.
Hence, Option 3: Fall in imports -> Aggregate Demand is calculated as AD = C + I + G + (X - M), where C is consumption, I is investment, G is government expenditure, X is exports, and M is imports. Since imports (M) are subtracted in the formula, a fall in imports actually increases net exports (X - M), which leads to a RISE in Aggregate Demand, not a fall. All other options represent components that are added to AD, so their fall would decrease AD. -> correct