有如下程序：#include#includeusing namespace std;class MyString{public; char str[80]; MyString(const char*s) {strcpy(str,s);} MyString&operator+=(MyString a){ strcat(str,a.str); return*this; }};ostream&operator<<(ostream&s,const MyString&z){return s << z.str}int main(){ MyString x("abc")，y("cde")； cout<<(x+=y)<

A．abc

B．cde

C．abcde

D．abccde