This sentence implies three things: 1, some costly technology made some successes possible; 2, some people had been against using this technology; 3, different people had been defending its usage. The blank needs the word that describes the current position of people who defended the technology. Those people probably believe they had been right all along, as the technology proved useful, so the successes confirm their position.
Out of the possible answers, only (B) refers to confirming something. "Vindicate" means "to show that something is correct," and it fits the context perfectly.
The correct answer is (B).