user: ### NOW ANSWER:
Question: Which Opened has a Category of Diesel light rail?
Columns: ['City', 'System', 'Category', 'Daily ridership', 'As of', 'Opened', 'Stations']
Types: ['text', 'text', 'text', 'real', 'text', 'real', 'text']
Sample row: ['Vancouver, BC', 'SkyTrain (Vancouver)', 'ICTS', 354000.0, '2009', 1985.0, '47']
SQL:

assistant: SELECT MAX("Opened") FROM "Table" WHERE "Category" = 'Diesel light rail';