Demand for a good is a measure of the relationship between
a) the price of that good and the quantity demanded of a substitute good
b) the price of that good and the general income level across a region
c) the price of that good and the quantity demanded of that same good when the determinants of demand do not change
d) the price of a particular good and the general educational level across a region
e) the price of that good and the quantity demanded for a complementary good