Final answer:
The PRI ruled in Mexico from 1929 to 2000, dominating the country's politics as a one-party state and implementing significant reforms including supporting labor unions and nationalizing the oil industry.
Step-by-step explanation:
The PRI (Institutional Revolutionary Party) ruled in Mexico from 1929 until 2000. The Mexican Revolution began in 1910, leading to a series of revolutionary generals taking power until the formation of the PRI in the 1920s, which intended to establish a more stable governing body. After the party's establishment, it continued to dominate Mexican politics for the rest of the 20th century, despite being a de facto one-party state with all presidents and the vast majority of the legislature hailing from the PRI.
Notably, President Lázaro Cárdenas, who assumed office in 1934, was a member of the PRI and introduced significant reforms, such as supporting labor unions, nationalizing the oil industry, and promoting land reform. Thus, the correct answer to the question of during what time period did the PRI rule in Mexico is option 2) 1929-2000.