user: Question: On how many different dates was event 1 Suspension Bridge?
Columns: ['Episode Number', 'Air Date', 'Event 1', 'Event 2', 'Event 3', 'Event 4']
Types: ['real', 'text', 'text', 'text', 'text', 'text']
Sample row: [1.0, '30 March 2008', 'Gauntlet', 'Duel', 'Pyramid', 'Pendulum']
SQL:

assistant: SELECT COUNT("Air Date") FROM "Table" WHERE "Event 1" = 'Suspension Bridge';