Suppose that when the price of root beer rises 10%, the quantity of pizza demanded falls 20%. This would mean that pizza and root beer are
a. compliments, with a cross elasticity of 0.5.
b. compliments, with a cross elasticity of 2.0.
c. substitutes, with a cross elasticity of 0.5.
d. substitutes, with a cross elasticity of 2.0.