--Was his father very strict with him when he was at school?--Yes.He had never praised him ____..
--Was his father very strict with him when he was at school?
--Yes.He had never praised him ________ he became one of the top students in his grade.(Unit7-5)
A.after?B.unless?C.until?D.when
为什么选C不选B?其它选项错在哪里呢?请分析一下句型或语法.