请看下面例句里的before是否可以换成until呢？
She applied three times before she was finally admitted to the university.
在她最终被大学录取之前，她申请了三次。
首先要明白，从时间概念上来考虑,before 和 until 都是表示时间都表示主句的情景发生在从句
的情景之前，即主句动作选发生。
I started my meal before Adam arrived.
在亚当到达之前我就开始吃饭了。
The ambassador will not comment on the issue before consulting his government.
大使在咨询政府前不会对此事发表评论。
I disliked Tom until I got to know him.
在我了解汤姆之前,我一直不喜欢他。
The trade talks continued until midnight to reach a compromise.
贸易谈判持续到午夜以达成妥协。
但是，它们用法上却是有所区别：
第一,
带有until从句的肯定式主句中的谓语动词必须是持续性的, 若为否定式，可为瞬间动词。而带有before 从句的主句中的谓语动词, 可为瞬间动词或延续性动词，无特殊限制。试比较:
He watched TV until his mother came back.
他看电视直到妈妈回来。
I waited until he returned.
我一直等到他回来。
According to scientists, dinosaurs dominated the earth for 150 million years until they suddenly vanished 65 million years ago.
据科学家称，恐龙在地球上统治了1.5亿年，直到6500万年前突然消失。
She waited in the lobby until he arrived.
她在大堂等待直到他到达。
We played chess until midnight.
我们下棋直到午夜。
否定结构：not...until表示“直到……才”，主句动作在从句动作前未发生。
- 例句：
I didn’t finish work until 9 o’clock last night.
我昨晚直到9点才完成工作。
He left for Wuhan before eight.
他八点前动身去武汉。
I shaved before I went to the party.
在参加宴会之前,我刮了胡子。
He almost knocked me down before he saw me.
他差点撞到我才看见我。
第二,
until 引出的分句的内容是真实的,而before引出的分句的内容可能是真实的,也可能是非真实的。
Let's wait until the rain stops.
我们等到雨停吧。
They dated for three years until they finally got engaged.
他们相恋三年后终于订婚。
And before she could speak again I began to talk.
她尚未再开口,我就开始说话了。
Pigs will fly before he’ll become a mathematician.
他要是能当数学家,猪都会K了。
所以，在开篇提出的例句里只能用before而不能用until，是因为 apply(申请)是个瞬间动词。大家都知道,until 与肯定主句连用时,主句中的动词不能是瞬间动词(start, finish),而必须是持续动词如 be，live，love. like, wait 等。
第三、
互换条件
- 否定句中：主句为否定式瞬间动词时，before与until可互换，但语义侧重不同。
- 例句：
The children won’t come back until/before it is dark.
孩子们直到天黑才回来。
- 肯定句中主句瞬间动词：只能用before。
- 例句：
We arrived there before it started to rain.
我们在下雨前到达那里。
Someone called me up in the middle of the night, but they hung up before I could answer the phone.
半夜有人给我打电话，但我还没来得及接电话，电话就挂断了。
I will try to finish this work before you can come.
我会尽量在你来之前完成这项工作。
强调动作迟缓性：只能用before，常与时间段状语连用。
- 例句：
It was quite a long time before he found the elephant.
过了很久他才找到大象。
She realized her feelings for him before he moved away.
在他搬走前，她意识到了自己对他的感情。
小结：
- before：聚焦时间顺序，主句动作在从句前发生，可用于任何动词类型。
- until：强调动作延续，主句动作持续到从句时间点，肯定句需用延续性动词。
- 否定结构：not...until表示“直到……才”，not...before强调“在……前未做”。