Final answer:
An example of a social complementary asset is technology and service firms in adjacent markets.
Step-by-step explanation:
An example of a social complementary asset is Choice A) Technology and service firms in adjacent markets.
In the given context, technology refers to alternative methods of combining inputs to produce outputs. Technology centers like California's Silicon Valley have attracted manufacturing complexes along the coast, where computer companies have established software firms that further attract other new companies. This collaboration between technology and service firms in adjacent markets exemplifies a social complementary asset.
Other options such as training programs and distributed decision-making rights might be considered complementary assets in different contexts, but they do not directly represent social complementary assets in this particular scenario.