Task: Question Generation
Input (English): The first elected head of government was Cuauhtémoc Cárdenas. Cárdenas resigned in 1999 to run in the 2000 presidential elections and designated Rosario Robles to succeed him, who became the first woman (elected or otherwise) to govern Mexico City. In 2000 Andrés Manuel López Obrador was elected, and resigned in 2005 to run in the 2006 presidential elections, Alejandro Encinas being designated by the Legislative Assembly to finish the term. In 2006, Marcelo Ebrard was elected for the 2006–2012 period.
Output (English): Why did the first elected head of government of Mexico City resign?