The Demand Curve for a Normal Good Will Always Slope

The demand curve for a normal good will always slope downward because:

A) the substitution effect and the income effect reinforce each other,and the substitution effect always displays an inverse relation between price and quantity demanded.
B) the substitution effect and the income effect reinforce each other,and the income effect always displays an inverse relation between price and quantity demanded.
C) even though the substitution effect and the income effect move in opposite directions,the substitution effect dominates,and it always displays an inverse relation between price and quantity demanded.
D) even though the substitution effect and the income effect move in opposite directions,the income effect dominates,and it always displays an inverse relation between price and quantity demanded.