What is the appropriate 'type parameter' for this generic 'Order' class

All items in an assumed bookstore order management system implement interface Item. Here is the partial implementation of Item and a Book class:

interface Item {
 double getPrice();
//... more methods 
}

class Book implements Item {

 //.. more methods and cotr

 public double getPrice() {
     return price;
 }

 double price;
 // .. more fields
}

Order is a generic class that represents order of any item (any class that implements Item). We have hid part of the type parameter of Order ( see ____ below). Note that getCost method of Order calls getPrice() on field item. You have to give complete declaration of type parameter of Order.

class Order< I ____ > {

  Order(I i, int q) {
    item = i; 
    quantity = q;
  }

  double getCost() {
    return item.getPrice() * quantity;
  }

  I item;
  int quantity;
}

Which one of followings is the appropriate type parameter of Order that allows it be defined for any class that implements Item?