to keep the cost of the bus low to ensure that the bus will be easy to replace to provide ideas about how the bus will be built to ensure that people know how to drive the bus
I gave my students this multiple choice question: Company X makes 100 custom buses each year. Company Y makes 10,000 of one type of bus each year. Which of the following is the most likely reason a customer would buy a bus from company X instead of company Y?

Only one answer is correct among these 4 choices:
- to keep the cost of the bus low
- to ensure that the bus will be easy to replace
- to provide ideas about how the bus will be built
- to ensure that people know how to drive the bus

Could you tell me which one is correct?

to provide ideas about how the bus will be built