-- Was his father very strict with him when he was at school?

    --- Yes. He even didn’t praise him _____ he had become one of the top students in his grade.

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

-- Was his father very strict with him when he was at school?

    --- Yes. He even didn’t praise him _____ he had become one of the top students in his grade.

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