What will be the output of the following Java program?

package pkg;
class output 
{
    public static void main(String args[])
    { 
        StringBuffer s1 = new StringBuffer("Hello");
        s1.setCharAt(1, x);
        System.out.println(s1);
    }
}

A. A contract specifying a set of methods that a class must implement B. A class that cannot be instantiated C. A class that contains only static methods D. A subclass of the Object class

A. Interfaces cannot be implemented by classes B. Only abstract classes can implement interfaces C. No, a class can only implement one interface D. Yes, a class can implement multiple interfaces

A. class B. abstract C. interface D. extends

A. To declare abstract methods B. To provide a base class with common methods and fields C. To make a class final D. None of These