user: Question: What is the build date of the locomotives with a total produced less than 45 and a FB-2 model?
Columns: ['Model', 'Specification', 'Build date', 'Total produced', 'Wheel arrangement', 'Prime mover', 'Power output']
Types: ['text', 'text', 'text', 'real', 'text', 'text', 'text']
Sample row: ['FA-1', 'DL-208A, DL-208B', '1949-1950', 28.0, 'B-B', '12-244B', 'hp (MW)']
SQL:

assistant: SELECT "Build date" FROM "Table" WHERE "Total produced" < 45.0 AND "Model" = 'FB-2';