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Defines an interface for creating objects, allowing subclasses to decide which class to instantiate. Factory methods delay the instantiation of a class to its subclasses.What if there is a third level of support? . Is xun yu's help.　　当他发现一切都变得...A low temperature stop valve, Unlike Example 1, Comprises a valve body 1 and a valve cover 2, A valve stem 3 is arrange in that valve body 1, One end of the valve stem 3 is provided with a valve disc 4, The other end of the valve stem 3 is provided with an adjusting handwheel 5, A low portion of that disc 4 is provided with a guide sleeve 6, The guide sleeve 6 is fixed by means of a connecting piece and a spring pad 8, Between that disc 4 and the guide sleeve 6 is provide a valve seat 7, A packing assembly 9 is arranged between the valve stem 3 and the valve cover 2, the O-ring 10 is further arranged at the upper part of the packing assembly 9, the upper part of the O-ring 10 is provided with a packing gland 11, the valve body 1 is provided with an arc-shaped end face 12 which forms a line seal between the valve body 1 and the valve seat 7, and the contact end of the valve disc 4 and the valve seat 7 is provided with a water grain surface 41, the packing assembly 9 comprises a flexible graphite packing layer.1. Icmp/igmp flood attack (hping)