Which of the following statements about consumer behavior and demand are correct? (A) Microeconomics studies the behavior of individual agents like consumers and firms in isolation. (B) Consumer equilibrium is achieved when marginal utility per unit of expenditure is equal for all goods consumed. (C) A change in the price of a good leads to a shift in the demand curve, but does not change the quantity demanded. (D) The income effect of a price change refers to the change in demand for a good when income increases, assuming other factors remain constant.