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

Question | Dec 30, 2017 | nextptr 

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?