CREATE TABLE table_name_68 (propulsion VARCHAR, order_year VARCHAR, manufacturer VARCHAR)

What is the Propulsion for the model offered in 2003-2004 by neoplan usa?
SELECT propulsion FROM table_name_68 WHERE order_year = "2003-2004" AND manufacturer = "neoplan usa"
SELECT "propulsion" FROM "table_name_68" WHERE "2003-2004" = "order_year" AND "manufacturer" = "neoplan usa"