Type Checking in C#: typeof, GetType() or is — what and when to use?

Hello everyone. I'm a beginner C# developer and I constantly get confused with type checks. There are three ways: `typeof`, the `GetType()` method, and the `is` operator. For example, I have this code: ```csharp object obj = "Hello"; // Option 1 if (obj.GetType() == typeof(string)) Console.WriteLine("This is a string via GetType"); // Option 2 if (obj is string) Console.WriteLine("This is a string via is"); // Option 3 Type t = typeof(string); ``` It seems like all three check the type, but I notice strange behavior. When I use `is` with nullable types, it behaves differently than `GetType()`. For example: ```csharp int? x = 5; if (x is int) // true Console.WriteLine("x is int"); if (x.GetType() == typeof(int)) // also true Console.WriteLine("x.GetType == typeof(int)"); ``` But if x = null, then `x is int?` returns false, and `GetType()` will throw a NullReferenceException. Also, I read that `typeof` works only with types at compile time, while `GetType