user: Question: What type has Rest day as a course and was on 21 May?
Columns: ['Date', 'Course', 'Distance', 'Type', 'Winner']
Types: ['text', 'text', 'text', 'text', 'text']
Sample row: ['13 May', 'Milan', 'km (mi)', 'Team time trial', 'Renault-Elf']
SQL:

assistant: SELECT "Type" FROM "Table" WHERE "Course" = 'Rest day' AND "Date" = '21 May';