to change是不定式作目的状语.
did you say中的you是主语,did...say 是谓动.
句意: 你刚才说了什么使他改变了主意?
until, before主句中要是有not 一定会用until吗? 一般情况是这样,但不是绝对的.
如: He didn't go to bed until his mother came back .
直到妈妈回来他才上床睡觉.
You can't continue the training until you have recovered from your cold .
直到你的感冒恢复了, 你才能继续训练.
You can't leave before 5 o'clock this afternoon .