下面选项中最应该是工具类的是：
选项：

A:class Telephone { public: void callTo( ); void callBy( ); private: /* 略 */ };
B:class IComputer { public: static const int xx = 1; public: virtual ~IComputer( ); virtual void runApp( ); virtual void showVideo( ); };
C:class Mobile:public Telephone,public IComputer { public: void callTo( ); void callBy( ); virtual void runApp( ); virtual void showVideo( ); };
D:class Package { public: static void PackBinary( ); static void PackText( ); static void PackPicture( ); static int getVer( ); private: static int version; };