The member access about template derivation

[guevara]

There are two templates. One is base, another is child

//Base.h

template<typename T> class Base
{
    protected:
    int x;
    char c;
};

//A.h

#include "Base.h"

template<typename T>class a: public Base<T>
{
    public:
    void test();
};

//A.cpp

#include "A.h"

template<typename T> void a<T>::test()
{
    x++;
}

These is an error in the file "A.cpp".
The compile message is: error: 'x' was not declared in this scope.
How can I solve this problem? Thanks a lot.