Read the following passage and answer the questions.Passage 1For most people learning to drive, the driving test arises ahead as a major barrier. It is also a general source of conversation whenever drivers are gathered together. There are probably more tall stories about the driving test than about any other motoring subjects; the most remarkable thing about those stories is the number of times the old ones appear again, years after they were first heard, in new and exaggerated forms. All driving examiners have had to pass a very strict selection process, followed by at least six weeks’training. In the course of this training the Department makes sure that their driving is of a consistently high standard.Driving test centers are chosen with equal care. It would be nice to have centers and examiners town by town. But this is just not possible, because the centers have to be at places where there is enough parking space for candidates (考生) and where there are enough test routes. Routes are carefully chosen to make sure that they are all roughly comparable—the proportion of right and left turns, hills, pedestrian (行人) crossings and so on. The object of all this is to make sure, as far as possible, that all candidates in the driving test have to cope with the same sort of conditions whether they take the test in New York or California.The work that examiners do in actually carrying out tests is checked continuously by supervising examiners. This is to make as sure as possible that every candidate for the driving test has a proper and equal chance of showing the examiner, in the words of the Regulations, “that he is competent to drive without danger to and with due consideration for other users of the road.”This is all that the examiner is concerned with.3.There isn’t a test center in every town because ________.