Answer:
C. Negative; Positive
Step-by-step explanation:
If soda and sandwiches are complementary goods, then the cross price elasticity between them is negative. Negative cross price elasticity indicates that an increase in the price of soda would result in a fall in the quantity demand for sandwiches. On the other hand, a decrease in the price of soda would result in an increase in the quantity demanded for sandwiches.
If yogurt and sandwiches are substitute goods which means that yogart can be used in place of sandwiches or sandwiches can be used in place of yogurt. The cross price elasticity between the substitute goods is positive. Positive cross price elasticity indicates that an increase in the price of yogurt would result in an increase in the quantity demanded for sandwiches. On the other hand, a decrease in the price of yogurt would result in a fall in the quantity demanded for sandwiches.