// 第一题
            string s1 = Console.ReadLine();
            char[] arr = s1.ToCharArray();
            Array.Reverse(arr);
            s1 = new string(arr);
            Console.WriteLine(s1);

            // 第二题
            string s2 = Console.ReadLine();
            s2 = s2.Replace("no", "yes");
            Console.WriteLine(s2);

            // 第三题
            string s3 = "I love you";
            StringBuilder result = new StringBuilder();
            foreach (var s in s3.Split(' '))
            {
                result.Append("\"" + s + "\"");
            }
            s3 = result.ToString();
            Console.WriteLine(s3);

            Console.ReadKey();