Which of the following statements is true?

a.  If the income elasticity of demand is less than zero, the good is an inferior good.

b.  Only if the demand curve is vertical will sellers raise the price by the full amount of a tax.

c.  Two goods are substitutes if the cross-elasticity of demand coefficient is positive.

d. A price elasticity of supply coefficient equal to 1.5 means the product exhibits an elastic supply and a 10% increase in the price will increase the quantity supplied by 15%.

e.  All of the above.