Extract Sentences Containing Certain Word

using System;
using System.Collections.Generic;
using System.Text;
using System.Text.RegularExpressions;

  class ExtractSentencesContainingCertainWord
{
    //Write a program that extracts from a given text all sentences containing given word.
        //Example: The word is "in". The text is:
    //We are living in a yellow submarine. We don't have anything else. Inside the submarine is very tight. So we are drinking all the day. We will move out of it in 5 days.
    //The expected result is:
    //We are living in a yellow submarine.
    //We will move out of it in 5 days.
    //Consider that the sentences are separated by "." and the words – by non-letter symbols.

  static List<int> FindSentencesWithWord(string[] sentences, string word)//Returns a list with the indices of the sentences that contain the searched word
  {
    List<int> sentencesToOutput = new List<int>();

    for (int i = 0; i < sentences.Length; i++)
    {
      if (Regex.Matches(sentences[i], "\\b" + word + "\\b",RegexOptions.IgnoreCase).Count > 0)
      {
        sentencesToOutput.Add(i);
      }
    }
    return sentencesToOutput;
  }

  static void Main()
  {
    string text = "We are living in a yellow submarine. We don't have anything else. Inside the submarine is very tight. So we are drinking all the day. We will move out of it in 5 days.";
    string word = "in";
    List<int> indecesOfwordInText = new List<int>();

    string[] sentencesArray;
    sentencesArray = text.Split('.');

    indecesOfwordInText = FindSentencesWithWord(sentencesArray, word);//Get the sentences that contain the word

    //Print on the console the found sentences
    for (int i = 0; i < indecesOfwordInText.Count; i++)
    {
      Console.WriteLine((sentencesArray[(indecesOfwordInText[i])] + ".").Trim()); //Add the dot and trim the emty spaces of each sentence that we are printing
    }

  }
}