not。。until 与not。。 before

until he has come 强调直到....才 是一种临界状态
直到他回来我才完成作业

before he came 强调再他回来之前 我没法完成作业

我觉得应该选B吧，
A.UNTIL后面一般接瞬间动词。
C.意思不符合，当``````
D.和A差不多，其后要接具体瞬间时刻。

下列情况下宜用before不用until.

1.主句为肯定式，谓语为终止性动词时只用before.
For example:
1). He fell asleep before I could take off his clothes.
2). We arrived there before it started to rain.
3). The holiday came to an end before I knew it.
4). He almost knocked me down before he saw me.

2.主句谓语动词强调动作的迟缓性，只用before,这时常伴有时间段状语或时间段暗示。
For example:
It was quite a long time before he found the elephant.过了很长时间，他才找到大象。
We had walked a long way before we found some water.走了很长的路我们才找到水。
We had sailed for two days before we saw the land.航行了两天我们才发现陆地。
It was midnight before my brother came home.我哥哥直到半夜才回来。

3.如果强调从句谓语动作未发生就发生主句谓语动作，只用before,这时常译为“未及（不等）……就……”
For example:
1）We can leave early in the morning before it gets too