2. 为了让 Dog 类的构造函数能正确地调用其父类 Animal 的构造方法，横线线处应填入（ ）。

1class Animal {2public:3   std::string name;4 5   Animal(std::string str) : name(str) {6        std::cout << "Animal created\n";7     }8   virtual void speak() {9     cout << "Animal speaks" << endl;10   }11};12 13class Dog : public Animal {14   std::string breed;15public:16   Dog(std::string name, std::string b) : _________________, breed(b) {17        std::cout << "Dog created\n";18     }19   void speak() override {20     cout << "Dog barks" << endl;21   }22};23 24int main() {25   Animal* p = new Dog("Rex", "Labrador");26   p->speak();27   delete p;28   return 0;29}