user: Question: Who were the candidates when Ed Markey was the incumbent?
Columns: ['District', 'Incumbent', 'Party', 'First elected', 'Result', 'Candidates']
Types: ['text', 'text', 'text', 'real', 'text', 'text']
Sample row: ['Massachusetts 1', 'John Olver', 'Democratic', 1991.0, 'Re-elected', 'John Olver (D) 67.56% Matthew Kinnaman (R) 32.38%']
SQL:

assistant: SELECT "Candidates" FROM "Table" WHERE "Incumbent" = 'Ed Markey';