GMAT Critical Reasoning (CR) | Re: Citing the frequency with which gum disease and heart

I chose E in this one.
It reverses the cause and effect - people who already had heart problems develop the dental ones. This weakens the logic that the dental problems are the ones which cause the heart problems.
In B there is too much for me to assume... exercise is out of scope for this one, no?
When are we allowed to introduce new facts and when are we not?

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