问题
选择题
. It is difficult for us to learn a lesson in life __________ we’ve actually had that lesson.
A．until
B．after
C．since
D．when
答案
A。
until的意思是“直到……时”“在……之前”，如：We always have to wait until the last customer has left. 我们总得等着最后一位顾客离去。