context: Yesterday I had to go across town to the library to return some books . All my friends were busy and my car was in for repairs , so I had to take the bus . First thing was to see what bus I needed . I went over to my computer and pulled up the bus schedules for my city . I found the nearest bus stop and checked the bus lines that stopped there , then looked for the stop nearest the library . There was a bus that went to both stops , so I would n't have to change buses to get there . Next I found the next time the bus would be at the stop near my house , which was only 15 minutes from now . I grabbed the books and headed out to walk to the bus stop . I got to the stop about 5 minutes early and waited for the bus to arrive . It was only 2 minutes late , which is n't too bad . I climbed into the bus , paid the driver and found an empty seat . It was a pretty nice day , so I just sat there looking out the window until we got to the stop by the library . I got off the bus and went inside to return my books . It was a good bus ride , no problems with traffic at all .
question: Why did the bus arrive a few minutes late?
reference: They were behind schedule
candidate: Because it was late and the driver was late