单项选择题

执行语句序列 ofstream outfile("DATA.DAT"); if(...)cout<<"OK";else cout<<"FAIL"; 后,如果文件打开成功显示"OK",否则就显示"FAIL"。由此可知,上面if语句的…处的表达式应是

A.outfilfail()或outfile
B.outfilgood()或!outfile
C.outfilgood()或outfile
D.outfilfail()或!outfile