Answer:
a. Negative slopes
Step-by-step explanation:
A negative slopes indicate that there exist a negative relationship between price and quantity demanded of a particular good. This means that when price falls, more units of goods will be purchased by the consumer and vice versa.
A normal good is a type of good whose demand increases as a result of increase in consumer's income. In other words, the higher the income, the higher the quantity demanded of such good by the consumer and vice versa.
It follows that when there is an increase in wage or income of a consumer , more goods will be purchased by them except if there is an increase in the price of such good . When there is price increase for such good, consumer will switch to a substitute good.