The correct answer is D. Budget constraint.
An expansion path in the theory of production is a curve that shows the maximum output that can be produced for a given level of inputs. It is a graph of the production function, which shows the relationship between inputs and outputs. The budget constraint is a line that shows the combinations of goods and services that a consumer can afford given their income and the prices of goods and services.
Engel’s curve is a graph that shows the relationship between income and the quantity demanded of a good. It is downward-sloping, which means that as income increases, the quantity demanded of a good decreases. This is because as people have more money, they tend to spend a smaller proportion of their income on necessities and a larger proportion on luxuries.
The price consumption curve is a graph that shows the relationship between the price of a good and the quantity demanded of that good. It is upward-sloping, which means that as the price of a good increases, the quantity demanded of that good decreases. This is because as the price of a good increases, consumers have less money to spend on other goods, so they demand less of the good.
The income consumption curve is a graph that shows the relationship between income and the quantity demanded of a good. It is upward-sloping, which means that as income increases, the quantity demanded of a good increases. This is because as people have more money, they can afford to buy more goods.