C#对象引用对于非静态的字段、方法或属性，object.string()是必须的

amespace Traffic
{
class Program
{
static void Main(string[] args)
{
AddPassenger(new Compact());
AddPassenger(new SUV());
AddPassenger(new Pickup());
AddPassenger(new PassengerTrain());
}
static void AddPassenger(IPassengerCarrier Vehicles)
{
Console.WriteLine(Vehicle.ToString());
}
}
}

错误提示为：对象引用对于非静态的字段、方法或属性，object.string()是必须的？

static void AddPassenger(IPassengerCarrier Vehicles)
{
Console.WriteLine(Vehicle.ToString());

变量名都搞错了。。===》
Console.WriteLine(Vehicles.ToString());

static void AddPassenger(IPassengerCarrier Vehicles)
改成
public void AddPassenger(IPassengerCarrier Vehicles)

还有IPassengerCarrier是Compact，SUV，Pickup，PassengerTrain的父类么？