The examples of tools given by the author (high-tech running shoes and specialized machines) also enhance athletic performance. The author isn’t saying that things that enhance athletic performance should be banned; the author is just saying that nonaddictive drugs shouldn’t be banned.

The author believes that addictive drugs should be banned. But this is because they are physically harmful, not because they are unnatural. Also, the argument concerns nonaddictive drugs, so additional information about addictive drugs does not weaken the argument.

The argument is about whether or not nonaddictive drugs should be banned in sports; risk of death or injury in other areas of life is completely irrelevant to the specific claims made in this argument.

(D) demonstrates some benefits of other unnatural tools used in sports; this does not weaken the argument. This actually gives a reason that some unnatural things have a positive role in sports.

The author accepts that addictive drugs are banned because they are physically harmful; there is no information given on the physical impacts of nonaddictive drugs. If nonaddictive drugs are physically harmful, the argument that they shouldn’t be banned is much weaker.