before与that

B
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意思是在我们又一次见到之前已经过了两年。
it was 可以换成 it had been ，是同样的意思。
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如果是that。则是强调句。it was .... that ....
可以换成 We met again two years .显然是不通的。
所以如果要用that .
应该说It was two years ago that we met again.

before
before 一个很特殊的意思
才

两年后我们才再次见面。

that

我觉得是个强调句型.it was ......that

b,
如果是A的话那就是IT WAS THAT 的强调句了，调整一下就是we met again two years，缺个介词，所以选B，

Iy was 2 years before we mey again.表示时间的状语，在..之前后面接从句we met again

before

before
KK: []
DJ: []
prep.
1. 在...以前
Only two days remained before the examination.
考前只剩下两天了。
2. (指顺序、重要性等)在...之前,先于
Your name comes before mine.
你的名字在我之前。
Pride comes before a fall.
骄必败。
3. 由...考虑中
We will put the matter before the committee.
我将把此事提交委员会考虑。
4. 在...前面;在...面前
She said she had never spoken before an audience.
她说她从未在大庭广众讲演过。
ad.
1. 较早
Come at