question: For the year 1975, what is Propulsion, with a Number (quantity ordered) of 4756-4788 (33 buses)?
answer: SELECT fuel_propulsion FROM table_name_41 WHERE year = 1975 AND numbers__quantity_ordered_ = "4756-4788 (33 buses)"
context: CREATE TABLE table_name_41 (fuel_propulsion VARCHAR, year VARCHAR, numbers__quantity_ordered_ VARCHAR)