The correct answer is B) No appreciable wear has occurred, and the proper maintenance procedures should continue to be followed. The reasoning is that the illustration shows a thrust bearing with over 8 years of ahead running time, and the measurements indicate a small difference between "i1" (4 mm) and "i2" (1 mm), which suggests minimal wear. A wear rate of 1.6 mm per year (as indicated in option C) would be considered excessive for a thrust bearing with this much operating time. Therefore, option B is the correct answer, as the thrust bearing does not show signs of significant wear and the proper maintenance procedures should be continued. The other options are incorrect because option A incorrectly suggests the stops are worn, when the measurements indicate minimal wear on the thrust bearing itself. Option C proposes an excessive wear rate that is not supported by the information provided, and option D suggests a need for more frequent monitoring, which is not necessary based on the low wear rate indicated by the measurements.