If the goods are complementary like car and petrol, their cross elasticity is

The correct answer is A. Negative.

Complementary goods are goods that are used together and whose demand is therefore linked. For example, cars and petrol are complementary goods, because if the price of cars goes up, people will buy fewer cars, and therefore demand for petrol will also go down.

The cross elasticity of demand is a measure of how much the demand for one good changes in response to a change in the price of another good. For complementary goods, the cross elasticity of demand is negative, because the demand for one good goes down when the price of the other good goes up.

The other options are incorrect.

• Option B is incorrect, because the cross elasticity of demand for complementary goods is negative, not positive.
• Option C is incorrect, because the cross elasticity of demand for complementary goods is not zero.
• Option D is incorrect, because the cross elasticity of demand for complementary goods is not infinite.