static void Main(string[] args)
{
JuiceCup cup = new JuiceCup();
cup.Add("白开水");
cup.Items.ForEach(m => {
Console.WriteLine(m);
});
Console.ReadKey();
}
public static List <string> Add(this JuiceCup cup, string water)
{
cup.Items.Add(water);
return(cup.Items);
}