Step 1: Trace the mechanism step by step:
Lower CRR → banks keep less as mandatory reserves → more funds available to lend → credit expands via the money multiplier → money supply rises.
Step 2: Connect money supply to demand:
A larger money supply, other things equal, lowers the interest rate, which encourages both investment by firms and consumption by households — both are components of aggregate demand.
Step 3: Rule out the alternatives:
A price-level fall or no change in AD would require a contractionary, not expansionary, policy stance, which is the opposite of cutting CRR.
Final Answer:
Option B, rise in aggregate demand.