Read the following context and choose the best option to answer the question.
Context: I winced - the amount was around five hundred dollars . " No , " she said . " The doctors have written off any difference . All you 're responsible for is a $ 20 co - pay .
Question: Why might have the doctor write off the differences ?
Options: 
- Because that might have been the arrangement with the hospital .
 - Because that might have been the arrangement with the medical company .
 - Because that might have been the arrangement with the insurance company .
 - Because that might have been the arrangement with the my company .


Because that might have been the arrangement with the insurance company .