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.outfil good() 或outfile
C.outfilgood ()或!outfile
D.outfilfail()或!outfile