user: Question: What is the date Listed of the B & O Bridge in Washington?
Columns: ['Name', 'Built', 'Listed', 'Location', 'County']
Types: ['text', 'text', 'text', 'text', 'text']
Sample row: ['B & O Railroad Potomac River Crossing', '1894, 1931', '1978-02-14', 'Harpers Ferry, West Virginia', 'Washington']
SQL:

assistant: SELECT "Listed" FROM "Table" WHERE "County" = 'Washington' AND "Name" = 'B & O Bridge';