Question

in 1974, mexican chemist mario molina and us chemist f. sherwood rowland discovered that chemicals called cfcs were harmful to the ozone layer. their research was extremely influential in the fight against cfcs. it laid the foundation for a 1987 treaty that phased out the use of cfcs across the globe. 23 which choice completes the text with the most logical transition? a specifically, b regardless, c earlier, d however,

Explanation:

"Specifically" is used to introduce a more detailed or particular point. Here, it emphasizes the particularity of the research's impact on the fight against CFCs and the 1987 treaty. "However" indicates a contrast, "Regardless" means without being affected by something, and "Earlier" refers to a previous time, none of which fit the context as well as "Specifically".

Answer:

A. Specifically,