user: Question: Which class starts after 1939 and has a road number smaller than 3508?
Columns: ['NBR number', 'Year', 'Original operator', 'Class', 'Wheel arrangement', 'Road number', 'Location']
Types: ['real', 'real', 'text', 'text', 'text', 'real', 'text']
Sample row: [22880.0, 1922.0, 'New Zealand Railways', 'A B', '4-6-2', 745.0, 'Stratford']
SQL:

assistant: SELECT "Class" FROM "Table" WHERE "Year" > 1939.0 AND "Road number" < 3508.0;