5. If C1 and C2 are goods (i.e., objects for which more is preferred to less), then the indifference curves are downward sloping because: (a) a decrease in period-1 consumption requires a decrease in period-2 consumption if the HH is to remain indifferent. (b) an increase in period-1 consumption requires a decrease in period-2 consumption if the HH is to remain indifferent. (c) an increase in period-1 consumption requires an increase in period-2 consumption if the HH is to remain indifferent. (d) indifference curves do not cross one another