I have waited for her since _____.

A．two hours ago

B．two hours before

C．two hours’ time

D．two hours

已知类A有公用数据成员a，并重载了=运算符，且有A obj2;const A ptr*=
new A；则下列语句错误的是

A．ptr-＞a=100;

B．ptr=&obj2;

C．ptr++;

D．obj2=*ptr;