Given below are two statements, one labeled as Assertion (A) and the other as Reason (R): Assertion (A): A fall in price increases quantity demanded. Reason (R): Income and substitution effects operate in the same direction for normal goods. Choose the correct alternative:

Consider the following statements regarding the dynamics of consumer demand: Statement 1: Expansion of demand is characterized by a downward movement along an existing demand curve resulting specifically from a decrease in the price of the commodity. Statement 2: An increase in demand is represented by a rightward shift of the entire demand curve driven by non-price factors such as rising consumer income or changing preferences. Which of the following options is correct?

According to economic theory, demand curves typically have a negative slope primarily because: