Why is this question D? Why not A?

26) Many economists do not believe that network externalities lock consumers into the use of products that have technology inferior to other, similar products. These economists believe that A) consumers are always rational. B) there is no good evidence that switching costs exists C) the government will prevent products with inferior technology from being sold to consumers D) in practice, the gains from ulsing a superior technology exceed the losses consumers incur from switching costs