user: Question: What is the length for a Diesel engine with numbers of TBD (13 buses)?
Columns: ['Year', 'Make & Model', 'Length', 'Engine Type', 'Numbers']
Types: ['text', 'text', 'text', 'text', 'text']
Sample row: ['2000-2004', 'Orion VI', 'ft (m)', 'Diesel', '6000-6161 (160 buses)']
SQL:

assistant: SELECT "Length" FROM "Table" WHERE "Engine Type" = 'Diesel' AND "Numbers" = 'TBD (13 buses)';