单选题：What will be the output of the following C++ code?

What will be the output of the following C++ code?

Content of header file h1.h
------------------------------------------------
//h1.h

#include <iostream.h>

using namespace std;

namespace A
{

int func(int a)
{

cout<<"using namespace A";
return 2*a;
}
}
------------------------------------------------

Content of header file h2.h
------------------------------------------------

//h2.h

#include <iostream.h>

using namespace std;

namespace B
{

float func(float a)
{

cout<<"using namespace B";
return 2*a;
}
}
------------------------------------------------

Content of program.cpp
------------------------------------------------
#include <iostream.h>

#include <string.h>

#include "h1.h"

#include "h2.h"

using namespace std;

using namespace A;

using namespace B;

int main(int argc, char const *argv[])

{

/* code */
int a = 10;
float b = 10.0;
cout<<A::func(a)<<endl;
cout<<A::func(b);
return 0;
}
------------------------------------------------



A.using namespace A20
using namespace B20
B.using namespace A20
using namespace A20
C.using namespace A10
using namespace A10
D.using namespace A10
using namespace B10


答案：B