Among the options provided, the country that is not considered a transitional economy is d) Mexico.
A transitional economy refers to a nation that is moving from a centrally planned economy to a market-oriented economy. China, Russia, and Hungary have all undergone significant economic reforms over the past few decades, transitioning from state control to more market-driven policies. Mexico, however, has been operating within a market economy framework for a much longer period, especially since the implementation of the North American Free Trade Agreement (NAFTA) in the 1990s. Therefore, it does not fit the definition of a transitional economy like the other three countries do.