Original: De Vries obtained his PhD in 1989 from H. Daudt and H. Daalder on the article he wrote on "Ground Politics" (later made into a novel by the same name) and the educational essay "Cabinet Crisis in the Netherlands".
Simplified: De Vries was promoted and got his degree in 1989 from dr. H. Daudt. en dr. H. Daalder for the article he wrote on "Ground Politics and Cabinet Crisis in the Netherlands".