Simon thought his computer was broken _______ his little brother pointed out that he had forgotten to turn it on
A.untilB.sinceC.afterD.because在线课程A
解析：
本题考查连词。根据句意他一直以为电脑坏了，直到他弟弟告诉他忘记开机了；
not...until...意为“直到……才”。