The way to look at this is to focus on the paradox. We are trying to figure out why people who use sugar substitutes actually gain weight. They gain weight even though some of the food they consume has fewer calories.

Choice B is eliminated right out of the gate because you cannot explain a difference using something that is the same for both sides. It states is choice B that there is no added sugar in these items - hamburgers and french fries - to replace. So this cannot explain why those who use sugar substitutes actually gain weight because if they ate hamburgers and french fries before then nothing has changed. If they did not eat these things before nothing has changed. That is the problem with B, nothing has changed.

Let me give you an example, say you are applying to business school and the interviewer asks what makes you special and you reply, "I really want to go to business school." Do you see how this is a very poor answer? Not because it is offensive or silly or untrue, but because you named something that is the same for everyone applying to business school. You cannot explain a difference with something that is the same.

Or, an even better example, if I were trying to figure out why some people do better on the GMAT than others do. You cannot say that the people who do well get an 75 minutes for each section. Everyone does! You need a difference, such as "they study harder."

Answer Choice B fits the mode of "they get 75 minutes." Because nothing has changed with the use of the sweeteners, these are not even used in burgers and fries, this cannot explain how something new has happened - namely those who use the artificial sweeteners gain weight.

I wanted to explain this to you thoroughly because this is a point that can be used in many paradox questions like this one. Anytime you are seeking to explain a difference between two things, you need a difference in the answer choices.

A difference in the stimulus can only be explained by a difference in the answer choices.

By the way D gives you a very significant difference. The artificial sweetener users become addicted because, as we are told in the stimulus the sweeteners are 200 to 600 times sweeter than sugar. There is no need to assume that people who fit into answer choice D eat sugar as well as sweeteners, it says it there, "Because sugar substitutes are so sweet, those people who consume them regularly become addicted to sweetness of all types, including sugar."

Remember a difference in the stimulus can only be explained by a difference in the answer choices. You cannot explain why a certain athlete is the fastest by saying that she wears running shoes. Now a particular type of special new shoe, yes that might work as an answer....

Thanks David For the post.It has really given me a new perspecive to view Paradox Questions from.I now understand Choice B much better.

There is 1 last thing i wish to clarify.
The reason why I chose B was
Suppose a Person follows a Diet consisting of Burgers + Sugar for 2 months.His weight Initially is 50 Kgs
He gains weight of 2,5 Kgs each month because of the burgers + 2.5 Kgs Because of the Sugar.=5 Kgs of Weight Gain in 1 Month
In 2 Months Wt. Gain = 10 Kgs out of which 5 Kgs is because of the Burgers
His Weight Increases to 60 Kgs.
Now He changes to Sugar Substitute but continues to have Burgers for 1 Month
So His weight Increases 60 + 2.5=62.5 Kgs.
So He gains Weight of 2.5 Kgs in 1 Month
Pls tell where is the Flaw in My reasoning ? Was I assuming too Much .

In your case, earlier person gained 5kgs but after taking sweetener person gained only 2.5kgs BUT the stimulus says that person experiences net weight gain,i.e. w.r.t. the gain person used to have earlier. In your case person has lost the weight because of using sweeteners and hence there is NO PARADOX.

The point that David is trying is explain is that use of sweeteners in hamburgers cannot explain why person who started using sweeteners gained weight. Because consumption of hamburgers and hence calories associated with hamburgers would remain same. For this an option that relates what happens when sweeteners are taken would help.

Hope that helps.