Final answer:
The best piece of evidence is that city hospitals experienced a 6% drop in cases of heart attack and stroke since the ban on trans fats was enforced.
Step-by-step explanation:
The best piece of evidence that supports the claim that banning the use of trans fats in restaurants has improved the general health of city residents is option A) Since the ban was enforced, city hospitals experienced a 6% drop in cases of heart attack and stroke.
This evidence indicates that the ban on trans fats has had a positive impact on the health of city residents by reducing the occurrence of heart attacks and strokes.
Furthermore, this evidence directly links the ban on trans fats to an improvement in health, making it the strongest piece of evidence to support the claim.