A. More of the cars in Donia’s capital city were made before 1993 than after 1993. 错的原因在于其实看文中这句话have been required in all new cars in Donia since 1993, 看出new cars=made after 1993,所以文中告诉你Yet although the proportion of new cars in Donia’s capital city has always been comparatively high, 就直接否定了A.
as a result, nitrogen dioxide emissions have been significantly reduced throughout most of the country. 的出现,说明A提出的问题不可能出现。此处的重点应该是most of the country和capital city之间的区别。