149. --- 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. (2003北京)

　 A. after　　　　　　　　　　 B. unless　　　　　　　　　　　 C. until　　　　　　　　　　　　 D. when