ExtractSentencesByKeyword

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Text.RegularExpressions;
using System.Threading.Tasks;

namespace _02.ExtractSentencesByKeyword
{
    public class StartUp
    {
        public static void Main()
        {
            string word = Console.ReadLine();
            var pattern = @"\b" + word + @"\b";
            string[] sentences = Console.ReadLine()
                .Split(new char[] { '.', '!', '?' },StringSplitOptions.RemoveEmptyEntries)
                .ToArray();
            Regex regex = new Regex(pattern);
            for (int i = 0; i < sentences.Length; i++)
            {
                Match match = regex.Match(sentences[i]);
                if (match.Success)
                {
                    Console.WriteLine(sentences[i].TrimStart());
                }
            }
        }
    }
}