Помогите. Экзамен на C#.

string str = "sdffd";
int count = str.Distinct().Count();//3

            string [][]words = { new string[] {"sdfg","sdfrr"},
                                        new string[] {"aaar","sgggg"}};
 
            File.WriteAllLines("1.txt", words.Select(x => string.Join(" ",x))); 
          
            string [] wordsToArr = words.Cast<string>().ToArray();
            string last = wordsToArr.Last();
            string[] wordsBeginsWith = wordsToArr.Where(x => x[0] == last[0]).ToArray();

            int n = 3;
            string mess = "мама мыла раму папа пил водку";
 
            string [] words = mess.Split().Where(x => x.Length <= n).ToArray();//пил

int count = File.ReadAllLines("1.txt").Count(x => x.First() == x.Last());

1
Console.WriteLine(count);
 
2
foreach(string s in wordsBeginsWith)
Console.WriteLine(s);
 
3
foreach(string s in words )
Console.WriteLine(s);
 
4
Console.WriteLine(count);

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.io;
 
namespace ConsoleApplication3
{
    class Program
    {
        static void Main(string[] args)
        {
            foreach (string s in wordsBeginsWith)
                Console.WriteLine(s);
            string[][] words = { new string[] {"sdfg","sdfrr"},
                                        new string[] {"aaar","sgggg"}};
 
            File.WriteAllLines("1.txt", words.Select(x => string.Join(" ", x)));
 
            string[] wordsToArr = words.Cast<string>().ToArray();
            string last = wordsToArr.Last();
            string[] wordsBeginsWith = wordsToArr.Where(x => x[0] == last[0]).ToArray();
        }
    }
}

string last = wordsToArr.Last();
string[] wordsBeginsWith = wordsToArr.Where(x => x[0] == last[0]).ToArray();

foreach (string s in wordsBeginsWith)
Console.WriteLine(s);