Hi lsat2016,
Welcome to the Forum!!
There is no reason to suspect that (A) weakens the argument. The argument is essentially causal: the author observes a decrease in likelihood of serious injury since 1955, which coincides with the introduction of the new legislation. From this, the author concludes that the new legislation was responsible for the increased worker safety:
- Cause Effect
New Legislation Increased safety
This may be so, but answer choice (A) presents an alternative cause: technological innovation! This is an alternative cause that could easily explain the increased worker safety, weakening the argument.
Answer choice (E), by contrast, has no relation to this causal argument. Maybe workplace safety conditions have improved across all industries - so what? This could be the result of the same legislation that the author believes improved worker safety in the high-risk industries. If anything, since the legislation does not appear to target high-risk industries in particular, answer choice (E) can easily be interpreted as strengthening the conclusion of the argument.
Hope this helps!