user: Question: Who were the candidates when Jack Fields was the incumbent?
Columns: ['District', 'Incumbent', 'Party', 'First elected', 'Result', 'Candidates']
Types: ['text', 'text', 'text', 'real', 'text', 'text']
Sample row: ['Texas 1', 'Jim Chapman', 'Democratic', 1985.0, 'Re-elected', 'Jim Chapman (D) 62.2% Horace McQueen (R) 37.8%']
SQL:

assistant: SELECT "Candidates" FROM "Table" WHERE "Incumbent" = 'Jack Fields';