问一个面对对象中的问题，在线等
class Building(){
public class Barn extends Building{
Building build1=new Building();
Barn barn1=new Barn();
Barn baen2=new Barn();//10
Object obj1=(Object)build1;//11
String str1=(String)build1;//12
Building build1=(Building)barn1;//13
}
}
a 如果第10行删除 the compilation succeds
b 如果第11行删除 the compilation succeds
c 如果第12行删除 the compilation succeds
d 都不能删除
[最优解释]
