SELECT "Fuel Propulsion" FROM table_71699 WHERE "Fleet Series (Quantity)" = '04001-04125 (125)'
Which Fuel Propulsion has a Fleet Series (Quantity) of 04001-04125 (125)?
CREATE TABLE table_71699 (
    "Builder" text,
    "Model" text,
    "Length (ft/m)" text,
    "Order Year" text,
    "Fuel Propulsion" text,
    "Fleet Series (Quantity)" text
)