阅读以下说明和C++代码，填补代码中的空缺，将解答填入答题纸的对应栏内。
[说明]
在股票交易中，股票代理根据客户发出的股票操作指示进行股票的买卖操作。其类图如下图所示，相应的C++代码附后。

类图

[C++代码] #include＜iostream＞ #include＜string＞ #include＜vector＞ using namespacestd; class Stock { private: string name; int quantity; public: Stock(stringname,int quantity) {this-＞name=name;this-＞quantity =quantity;} void buy() {cout＜＜"[买进]股票名称:"＜＜name＜＜",数量:"＜＜quantity＜＜ endl;} void sell() {cout＜＜"[卖出]股票名称:"＜＜name＜＜",数量:"＜＜quantity ＜＜endl;} }; clasS order{ public: virtual voidexecute()=0; }; classBuyStock:______ { private: Stock* stock; public: BuyStock(Stock*stock){______ =stock; } void execute(){ stock一＞buy(); } }; //类SellStock的实现与BuyStock类似,此处略 class Broker{ private: vector＜Order*＞ orderList; public: voidtakeOrder(______ order)( orderLiSt.push back(order);} void placeorders() { for(int i=0;i＜orderList.Size(); i++){______ -＞execute();} 0rderLiSt.clear(); } }; classStockCommand{ public: VOid main(){ Stock* aStock=newStock("股票A",10); Stock*bStock=newStock("股票B",20); Order*buyStockOrder=new BuyStock(aStock); Order*sellStockOrder=new SellStock(bStock); Broker* broker=newBroker(); broker-＞takeOrder(buyStockorder); broker-＞takeOrder(sellStockOrder); broker-＞ ______ (); } }; int main(){ StockCommand*stockCommand=new StockCommand(); StockCommand-＞main(); deleteStoCkCommand; }