function Animal(name) { 

    this.name = name;

 } 

 Animal.prototype = {

    weight: 0, 

    eat: function() { 

        alert( "Animal is eating!" ); 

    } 

 }

 function Mammal() { 

    this.name = "mammal"; 

 } 

 Mammal.prototype = new Animal("animal"); 

 function Horse( height, weight ) { 

    this.name = "horse"; 

    this.height = height; 

    this.weight = weight; 

 }

 Horse.prototype = new Mammal(); 

 Horse.prototype.eat = function() { 

    alert( "Horse is eating grass!" ); 

 }

 var horse = new Horse( 100, 300 ); 

问题：

1. Horse.prototype===？为true

2. Mammal.prototype===？为true

3. Animal.prototype===？为true