Which statements， when inserted at the indicated position in the following code， will cause a runtime exception when attempting to run the program？（）  
class A {}  
class B extends A {}  
class C extends A {}  
public class Q3ae4 {  
public static void main（String args[]） { 
 A x = new A（）； 
 B y = new B（）；  
C z = new C（）；  
// insert statement here  
}  
} 

Which is the earliest line in the following code after which the object created on the line marked （0） will be a candidate for being garbage collected， assuming no compiler optimizations are done？ （） 
public class Q76a9 {  
static String f（） {  
String a = "hello"；  
String b = "bye"； // （0） 
 String c = b + "!"； // （1）  
String d = b；  b = a； // （2）  
d = a； // （3）  
return c； // （4）  }  
public static void main（String args[]） { 
 String msg = f（）；  
System.out.println（msg）； // （5） 
 }  
}  

Which statements can be inserted at the indicated position in the following code to make the program write 1 on the standard output when run？（） 
public class Q4a39 { 
int a = 1；  
int b = 1；  
int c = 1；  
class Inner {  
int a = 2；  int get（） {  
int c = 3；  
// insert statement here  return c； 
 }  
}  Q4a39（） {  
Inner i = new Inner（）；  
System.out.println（i.get（））；  }  
public static void main（String args[]） { 
 new Q4a39（）； 
 }  
}  

Which lines of code are valid declarations of a native method when occurring within the declaration of the following class？（）   
public class Qf575 {  
// insert declaration of a native method here 
 }  

What will be written to the standard output when the following program is run？（）  
class Base {  int i；  Base（） {  
add（1）；  
}  
void add（int v） {  i += v；  }  
void print（） {  System.out.println（i）；  }  
}  
class Extension extends Base {  Extension（） {  add（2）；  }  
void add（int v） {  i += v*2；  }  }  
public class Qd073 {  
public static void main（String args[]） {  bogo（new Extension（））；  }  
static void bogo（Base b） {  b.add（8）；  b.print（）；  
}  
}