string str1 = "Hello"; string str2 = "World"; str1 = str1.Append(str2); // Output should be "HelloWorld"
string str = "Hello"; char c = '!'; str = str.Append(c); // Output should be "Hello!"
string str = "Hello"; string[] arr = {" ", "World", "!"}; str = str.Append(arr); // Output should be "Hello World!"