How does aggregate demand curve (AD) differ from an individual demand

How does aggregate demand curve (AD) differ from an individual demand curve (D)?

A) AD is generally vertical while D is usually downward sloping.
B) D represents the price-quantity relationship for a single good or service while AD looks at the entire economic system.
C) AD is generally a downward sloping curve while D usually slopes upward.
D) Look for D in macroeconomic analyses and for AD in microeconomics.

ANSWER

B