user: Question: Name the date which has type of Plain stage
Columns: ['Date', 'Course', 'Distance', 'Type', 'Winner']
Types: ['text', 'text', 'text', 'text', 'text']
Sample row: ['20 May', "Campione d'Italia", 'km (mi)', 'Individual time trial', 'Charly Grosskost ( FRA )']
SQL:

assistant: SELECT "Date" FROM "Table" WHERE "Type" = 'Plain stage';