The management of urban water networks is a difficult problem. To discover the problems of urban water networks, you can only judge by the personal experience of plumbers or their field investigations. Based on the above information, can we be sure? ['Without plumbers will not be able to discover the problem of the water network of the teacher.', 'Problems with urban water networks would not be possible without a field survey.', 'Judgement of the personal experience of plumbers is sufficient to identify problems with urban water networks.', 'Field surveys can reveal problems with urban water networks.']