These two events are an example of Correlation.
A.Correlation
Explanation:
The development of Henry Bessemer's invention was made possible only because of Abraham Darby's invention. Abraham Darby's invention was the cast iron so the cast iron is important for making the steel production . so the invention of Abraham Darby is important for the Henry Bessemer invention.
Because of this, both the inventions are only correlated with one another since they do not form a cause and effect relationship between them. The cast iron is the basement of the steel production.