严格意义上说 It was .that.才是句式 表强调.这个句式跟not until 没有关系的
eg.:it was not until yesterday that we arrived there.（直到昨天我们才到那里）
该强调句式表达的最大特点是 将句中 it was 和 that去掉 句子仍然完整 无语病.
你后面提到的It was not until.when.也一样 它不是某一个固定的句式.
只是比较常放在一起用 很多人便认为是一起的.
这样句子可以造出来 但是记住它们并非是连成一体的句型
如：it was not until late at night when you had already fell asleep that we arrived there.
直到夜深了,你早已入睡,我们才到那里.
不知道我表达的够不够清楚 欢迎追问It was not until last year _______ their plan was approved. A.whenB.that此题的答案给的是：A不知怎么解释？谢谢你确定是A么个人觉得是that It was not until last year thattheir plan was approved.表示强调。去掉it was和 that ：Notuntil last year ， their plan was approved.