单选题

请指出下列代表有几处错误。

Question

请指出下列代表有几处错误？

#include <stdio.h>
class A
{
    public:
      virtual void f(){}
    public:
       A()
       {
           f()
       }
}

class B1:public A()
{
    private:
        char *_s
    public:
        B1()
        {
            _s=new char[1024]
        }
    private:
        void f()
        {
            delete _s[]
            _s=NULL
        }
}

class B2:public A
{
    private:
        int * _m
    public:
        B2()
        {
            _m=new int(2016)
        }
    private:
        virtual void f()
        {
            delete _m
            _m=NULL
        }
}
int main()
{
    A *a1=new B()
    A *a2=new C
    delete a1
    delete a2
    return 0
}

A. 3

B. 4

C. 5

D. 6