Final answer:
The O-ring theory places emphasis on skill complementarities, where the productivity in complex processes is interdependent on various skills, similar to how an O-ring's failure can affect a whole system.
Step-by-step explanation:
The O-ring theory places emphasis on skill complementarities. It suggests that the productivity of workers in complex production processes is highly interdependent; similarly to how an O-ring can cause a failure in an otherwise complex system, the lack of skill in one area can significantly affect the overall performance. The theory was proposed by Michael Kremer in 1993, and it is often used to explain issues of quality and technology transfer, especially in developing countries. The emphasis is not on education or the purchase of machinery alone, but on the degree to which various necessary skills are complementary in production. Hence, the correct answer is b. skill complementarities.