Which of the following is the correct way to implement a read only property Length in a Sample class?

• class Sample { int len; public int Length { get { return len; } } }
• class Sample { public int Length { get { return Length; } } }
• class Sample { int len; public int Length { get { return len; } set { len = value; } } }
• class Sample { int len; public int Length { Readonly get { return len; } } }