StringBuilder sb = new StringBuilder();

sb.Append("This is the start of a very long string. ");
sb.Append("It just gets longer and longer. ");
sb.Append("When will this end?");
sb.Append("No one knows.");
sb.Append("Can you find the Banana in this string. ");
sb.Append("Only you can find it and save the world. ");
sb.Append("Now go and bring back the results.");

Boolean result = sb.ToString().Contains("Banana");