user: Question: Which prime mover had a Model of RS-18?
Columns: ['Model', 'Specification', 'Build date', 'Total produced', 'Wheel arrangement', 'Prime mover', 'Power output']
Types: ['text', 'text', 'text', 'real', 'text', 'text', 'text']
Sample row: ['RS-1', 'ME1000R (E-1641A)', '1954', 3.0, 'B-B', '6-539T', 'hp (kW)']
SQL:

assistant: SELECT "Prime mover" FROM "Table" WHERE "Model" = 'RS-18';