Ошибка: cannot call member function

#ifndef MCT_H
#define MCT_H
#include <string>
 
class MCT
{
private:
 
    static std::string FirstString;
    static std::string SeacondString;
 
public:
 
    MCT();
 
    void PrintFS ();
    void PrintSS ();
    bool AddFS(std::string InputString);
    bool AddSS(std::string InputString);
};
 
#endif // MCT_H

#include "mct.h"
 
MCT::MCT()
{
 
}
 
 
MCT::PrintFS ()
{
    if (FirstString.size()==0) std::cout << "FirstString is NULL\n";
    std::cout<< FirstString << std::endl;
}
 
MCT::PrintSS ()
{
    if (FirstString.size()==0) std::cout << "FirstString is NULL\n";
    std::cout<< FirstString << std::endl;
}
 
MCT::AddFS(std::string InputString)
{
    FirstString=InputString;
//    if (FirstString==InputString) return false;
    return true;
}
 
MCT::AddSS(std::string InputString)
{
    SeacondString=InputString;
//    if (SeacondString==InputString) return false;
    return true;
}

#include <iostream>
#include <string>
 
#include "mct.h"
 
using namespace std;
 
int main()
{
    new MCT;
 
    MCT::AddFS("test 1");
    MCT::AddSS("test 2");
 
    MCT::PrintFS();
    MCT::PrintSS();
 
 
    return 0;
}