The correct answer is A. Coke will rise.
The demand for a good is the amount of that good that consumers are willing and able to purchase at different prices. The law of demand states that, all other things being equal, the demand for a good will decrease as the price of that good increases. This is because consumers are generally willing to purchase more of a good when it is cheaper.
In this case, the price of Pepsi has decreased relative to the price of Coke and 7-Up. This means that Pepsi is now relatively cheaper than Coke and 7-Up. As a result, consumers will be more likely to purchase Pepsi instead of Coke or 7-Up. This will lead to an increase in the demand for Pepsi and a decrease in the demand for Coke and 7-Up.
Option B is incorrect because the price of 7-Up has not changed. Therefore, there is no reason to expect the demand for 7-Up to change.
Option C is incorrect because the demand for both Coke and 7-Up will decrease.
Option D is incorrect because the demand for both Coke and 7-Up will decrease.