Member function of (public) derived class is inaccessible from main

I have four classes (classic diamond problem in C++). Let's call the grandparent class A, the parent classes B and C and the child class D. Both B and C have a public member function called attack. I want D to use B's attack function. Class D looks like this:

class D : public B, public C
{
    using   B::attack;

    public:
        D(void);
        D(std::string &name);
        D(D &instance);
        ~D(void);

        D&      operator=(D &instance);

};

The attack function simply displays a message on the standard output. My main looks like this:

int     main(void)
{
    DiamondTrap dt;
    dt.attack();
}

The error I get is the following:

error: 'attack' is a private member of 'D'

note: implicitly declared private here
        using   B::attack;

Does this mean that using using keyword makes member functions private? I don't know why attack is now private. I can call attack it in my main function from an instance of B, but not from an instance of D. I wish to call it from an instance of D. How can I solve this?

Note I don't know if this is relevant to my problem, but B and C's inheritance is virtual, so only one instance of A is created when an instance of D is created. Also, I am not allowed to use friend keyword in my solution, and I am only allowed to use C++98.