user: Question: What is the average total produced when the prime mover is 12-251C?
Columns: ['Model', 'Build date', 'Total produced', 'Wheel arrangement', 'Prime mover', 'Power output']
Types: ['text', 'text', 'real', 'text', 'text', 'text']
Sample row: ['C-424', '1963–1967', 92.0, 'B-B', '16-251B', 'hp (kW)']
SQL:

assistant: SELECT AVG("Total produced") FROM "Table" WHERE "Prime mover" = '12-251C';