We would expect the cross elasticity of demand between Pepsi and Coke to be (a) positive, indicating normal goods (b) positive, indicating inferior

We would expect the cross elasticity of demand between Pepsi and Coke to be

(a)

positive, indicating normal goods

(b)

positive, indicating inferior goods

(c)

positive, indicating substitute goods

(d)

negative, indicating substitute goods

i want to know why and how to get that answer, thank you.