有关untilyuunless的区别？

Question

Though he was disabled, he was never satisfied ______ he did the best of a normal child.
A. until B. unless
请问到底选哪个？为什么？

Answer 1

Though he was disabled, he was never satisfied until he did the best of a normal child. 虽然他残废了，但是他却像个正常孩子那样，一直努力做到最好为止。

选A。until是“直到……时”，而unless则是“除非”的意思。