Demand curves are derived while holding constant ........

Explanation:

• In the short-term, the price will remain the same and the quantity sold will increase. The same effect occurs if consumer trends or tastes change. This means more of the good or service are demanded at every price. When the economy is booming, buyers' incomes will rise.
• The demand curve is derived by analyzing the relationship between own price of a good and its quantity demanded while keeping other demand factors as constant. Other demand factors include the price of related goods, income, and taste and preferences of consumers.
• Note: Price of related goods is held constant as it cannot explain the up and down movement on the demand curve.
• Suppose the price of doughnuts were to fall. Many people who drink coffee enjoy dunking doughnuts in their coffee; the lower price of doughnuts might therefore increase the demand for coffee, shifting the demand curve for coffee to the right.

Hence option 3rd is correct.