下列类D代码段出现编译错误，原因是【 】。 include＜iostream. h＞ class A { public: A(char c){cout＜＜'A's constructor.'＜＜c＜＜endl;} ～A(){cout＜＜'A's destructor.'＜＜endl;} }; class B: virtual public A { public: B(char cb,char cd):A(cb) {cout＜＜'B's constructor.'＜＜cd＜＜endl;} ～B(){cout＜＜'B's destructor.'＜＜endl;} private: char b; }; class C:virtual public A { public: C(char cc, char cd):A(cc) {cout＜＜'C's constructor. '＜＜cd＜＜endl;} ～C(){cout＜＜'C's destructor.'＜＜endl;} }; class D:public B,public C { public: D(char cd,char ce,char cf, char cg, char ch,char ci) :C(cf,cg),B(cd,ce),A(cd),aa(ch) {cout＜＜'D's constructor.'＜＜ci＜＜endl;} ～D() {cout＜＜'D's destructor.'＜＜endl;} private: A aa; }; void main() { D ohj('a','b','c','d','e','f') }