How to generate random strings without repeating [duplicate]

string[] thing; 
thing = new string[5] { " Element 1 ", " Element 2 ", " Element 3 ", " Element 4 ", " Element 5 " };

Random r = new Random();
       
string randomString = "";
        
randomString += thing[r.Next(0, 5)].ToString();
        
        
        textBox1.Text += randomString;