I don't understand the following exercise. Thanks in advance for help

20. An increase in the demand for vacation motor homes could be caused by

1. an increase in the price of gasoline.
2. a reduction in interest rates.
3. a decrease in rental rates for motel rooms.
4. a reduction in the price of motor homes.
5. lower plane fares.

21. A 1000$ per automobile pollution tax on the manufacturer will shift the:

1. supply curve up (to the left) by 1000$.
2. demand curve up (to the right) by 1000$.
3. supply curve down (to the right) by 1000$.
4. supply curve and demand curve down (to the right) by 1000$.

24. The development of technology and the internet has allowed students to earn their degrees in the online environment. How has this technology effected the market for university or college level courses?

1. Increased demand
2. Decreased demand
3. Increased Supply
4. Decreased supply

28. If the quantity demanded is not very responsive to changes in price, then demand is said to be:

1. uncooperative
2. inelastic
3. elastic
4. substitutable

31. An increase in the price of leather is expected to cause:

Select one:

1. a fall in the supply of leather chairs
2. an increase in the demand for leather chairs
3. a fall in the demand for leather chairs
4. an increase in the supply of leather chairs