The correct answer is: C. efficiency curve.
An efficiency curve is a curve that shows all the combinations of goods and services that can be produced with a given amount of resources. It is also known as a production possibility frontier (PPF). The PPF is a downward-sloping curve because as more of one good is produced, less of the other good can be produced.
The attitude towards risk is a measure of how willing an investor is to take on risk. Investors who are more willing to take on risk are said to be more aggressive, while investors who are less willing to take on risk are said to be more conservative.
The return trade-off function is a function that shows the relationship between risk and return. The return trade-off function is upward-sloping because investors expect to earn a higher return for taking on more risk.
A difference curve is a curve that shows all the combinations of goods and services that provide the same level of satisfaction to an individual. It is also known as an indifference curve. Indifference curves are downward-sloping because individuals are always willing to trade off some of one good for more of another good, as long as they are getting the same level of satisfaction.
An affectivity curve is a curve that shows the relationship between emotion and behavior. The affectivity curve is upward-sloping because people are more likely to engage in behavior that makes them feel good.
In conclusion, the correct answer is C. efficiency curve.