[问答题] 什么是IP子网，请简述IP子网划分的作用。

塔式起重机栏杆高度≧（）m ["1","1.2","1.5","0.9"] 需求工程的第一步是（），其目的是确定和理解不同用户的需要和限制的过程，因而需要与用户有效的交流。 氧化锌避雷器的特点是什么？ A Windows Communication Foundation (WCF) application uses a data contract that has several data members. You need the application to throw a SerializationException if any of the data members are not present when a serialized instance of the data contract is deserialized.What should you do?（） [" Add the KnownType attribute to the data contract. Set a default value in each of the data member declarations."," Add the KnownType attribute to the data contract. Set the Order property of each data member to unique integer value."," Set the EmitDefaultValue property of each data member to false."," Set the lsRequired property of each data member to true."] 次数分布表 什么是IP子网，请简述IP子网划分的作用。