I'm going to go with B. Just because "everyone is doing it" doesn't mean they know what they're doing. Coke spends a ton of money on advertising because they want more sales and common wisdom says the way to get more sales is to spend a ton of money on advertising. It might work, it might not, but it isn't a simple 1 to 1 thing and it works differently on different people.

On a personal note, I grew up drinking Coke (because my dad preferred it), and I generally prefer the taste of Coke most likely because it's what I grew up drinking. I've seen Coke ads, and I've seen Pepsi ads, and neither one makes me want to drink one or the other or go buy one or the other. About the only thing it might do is influence me to go get a Coke if I was already feeling a bit thirsty although even if it was a Pepsi ad it would probably still make me want to get a Coke. In this case it would be a win for Soda vs. some other kind of drink like say a Starbucks coffee, not specifically Coke vs. Pepsi.