Well done for writing your reasoning out so clearly. Let me see if I can diagnose your error.
First, you seem to mix up
assumptions and
premises. Be really clear that a premise is something (usually a fact) that is given to you in the argument to support the conclusion. An assumption is something that the argument needs to be true in order to work. Check out the assumptions chapter in the CR strategy guide for more on this.
Assumption 1: "licensing the use of its name for products involves some danger, since if the products disappoint consumers, the magazine's reputation suffers, with consequent reductions in circulation and advertising"
This is a premise.
So, for the magazine to maintain its revenues, no other products in the market overall have to be superior to the one carrying the Kitchen's name
You're making a big step here. Sure, we don't want to disappoint the customers, but does this mean that we have to get the
very best in the market? I don't think so. Take a simpler example: I give you a present of a pair of shoes. If they're poor quality shoes, then you're going to be disappointed, but that doesn't mean I have to give you the
best shoes in the world for you to be satisfied. I could just give you a pretty good pair.
Assumption 2: "However, experts have evaluated the cookware and found it superior to all other cookware advertised in Kitchen"
Again, this is a premise.
Stated otherwise, if in the market there is another line of cookware superior to that licensed by Kitchen (but not advertised in the Kitchen magazine, per assumption 2), then consumers will be disappointed with the licensed cookware, and thus, per assumption 1, they will stop buying the magazine and this will affect sales and advertising revenues.
This is where you go wrong. We don't know that the customers will be disappointed with a line of cookware that is not the very best.
Being really clear about what an assumption is will help out your CR. Answer A might well
strengthen the argument (the better the cookware, the happier people will be with it), but it's not
essential to the argument. Answer C, on the other hand, is essential: if other companies cease advertising, then the revenues will be affected.