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The author does not imply that recent advances are more threatening than past ones. Instead, he suggests that the nature of technological progress (with more individuals and smaller groups able to innovate) has changed, leading to new risks. The focus is not on comparing "past vs. recent" as more threatening but on the unexpected global impacts of all technological advances. Thus, option A misrepresents the author's view.
Option b: The author would agree with this because the passage explains that Ethyl (leaded fuel) and Freon are examples of innovations whose unintended consequences stem from by-products they emitted (such as lead from fuel and chemicals from Freon), which had secondary effects on health and the environment.
Option c: The author would support this as he mentions how individuals or small groups can now create innovations that have global impacts, particularly in fields like biotechnology and chemistry, which was less true in the past.
Option d: The author suggests that the health threats of leaded fuel were visible earlier (in the 1920s), implying that they should have been addressed sooner. Hence, the author would support this
Hence, option a is the correct answer.