The correct answer is A.
Substitute goods are goods that can be used in place of each other. When the price of one substitute good increases, the demand for the other substitute good will increase. This is because consumers will switch to the other good as a way to save money.
In this case, apples and oranges are substitute goods. When the price of apples increases, the demand for oranges will increase. This is because consumers will switch to oranges as a way to save money. As a result, the demand curve for oranges will shift to the right.
Option B is incorrect because a leftward shift in the supply curve of apples would cause the price of apples to decrease. Option C is incorrect because a downward change in the demand curve of oranges would cause the price of oranges to decrease. Option D is incorrect because a fall in the price of oranges would not be caused by a rise in the price of apples.