using System;

using System.Collections.Generic;

​

public class Program

{   

    public static void Main()

    {

        List<string> Titles= new List<string>(new string[] { "title1", "title2", "title3" });

        List<Book> Books = new List<Book>{new Book{Title = Titles[0], Author = string.Empty}, new Book{Title = Titles[1], Author = string.Empty}, new Book{Title = Titles[2], Author = string.Empty}};

        // ^ заменить предыдущую строку ^ //

        Console.WriteLine(Books[0].Title);

    }

}

​

public class Book

{

    public string Title { get; set; }

    public string Author { get; set; }

}