下面可以正确输出 They're planning a party for their friend's birthday. 的C++语句是？ （ ）
- A. cout << 'They\'re planning a party for their friend'\s birthday." << endl;
- B. cout << "They\'re planning a party for their friend's birthday.'<< endl;
- C. cout << 'They're planning a party for their friend's birthday.'<< endl;
- D. cout << "They\'re planning a party for their friend\'s birthday." << endl;
正确答案：D