We don’t need information about children without ADD. (A) is saying that the adrenaline rush is limited to children with ADD, but that still doesn’t connect adrenaline to the worsening of ADD in the causal way that we need.

We don’t need adrenaline to incite ADD, we need adrenaline to make the symptoms worse. The conclusion is about children that already have ADD and their symptoms worsening.

It’s unnecessary for sugar restriction to be the best way to treat ADD. If we negate this and assume something else to be the best treatment, it’s still completely possible that sugar makes ADD symptoms worse.

This must be true. If negated, then the support has nothing to do with the premises—there would be no reason to believe that sugar makes ADD worse, because the connection from ADD to adrenaline would be severed.

This does not build a bridge between adrenaline and ADD. (E) is essentially saying that the adrenaline-producing effect of sugar can be mitigated, but that isn’t necessary for the argument.