Make uppercase

Given a string, write a method that returns new string in which every odd letter of the word is uppercase. String may consist of one or more words.
Expected input and output
MakeUppercase("modem") → "MoDeM" MakeUppercase("BookWorm") → "BoOkWoRm" MakeUppercase("Aliquam dolor nisl?") → "AlIqUaM DoLoR NiSl?"
using System;

namespace CSharpExercises.Exercises.Strings
{
    class MakeUppercaseTask
    {
        public static string MakeUppercase(string word)
        {
            int letterIndex = 0;
            string uppercaseWord = string.Empty;

            for (int i = 0; i < word.Length; i++)
            {
                if (word[i] >= 'a' && word[i] <= 'z' && letterIndex % 2 == 0)
                {
                    letterIndex++;
                    uppercaseWord += (char)(word[i] - 32);
                }
                else if (word[i] != ' ')
                {
                    letterIndex++;
                    uppercaseWord += word[i];
                }
                else
                {
                    letterIndex = 0;
                    uppercaseWord += word[i];
                }
            }
            return uppercaseWord;
        }

        public static void Main()
        {
            Console.WriteLine(MakeUppercase("very short sentence."));   // VeRy ShOrT SeNtEnCe.
            Console.WriteLine(MakeUppercase("motorcycle"));             // MoToRcYcLe
            Console.WriteLine(MakeUppercase("Events And Delegates"));   // EvEnTs AnD DeLeGaTeS
        }
    }
}