user: Question: Which State (class) has a Successor of Harry F. Byrd, Jr. (D)? Question
Columns: ['State (class)', 'Vacator', 'Reason for change', 'Successor', "Date of successor's formal installation"]
Types: ['text', 'text', 'text', 'text', 'text']
Sample row: ['South Carolina (3)', 'Olin D. Johnston (D)', 'Died April 18, 1965', 'Donald S. Russell (D)', 'April 22, 1965']
SQL:

assistant: SELECT "State (class)" FROM "Table" WHERE "Successor" = 'Harry F. Byrd, Jr. (D)';