It wasn’t until nearly a month later----I received the manag

It wasn't until nearly a month later____I received the manager's reply.a.since b.when c.as d.that
原因是强调句,我的问题是：它之所以是强调句是因为选了D,由it wasn't和that组合后才构成强调句.那么如果不选D的话不就不是强调句了?如果当成普通的句子,when为什么不行?求英语专业高手详解.不要复制粘贴的答案,不要瞎猜的答案.

你把强调句 It was.that 去掉,还原一下
Not until nearly a month later did I receive the manager's reply.
否定词放句首,倒装
如果把倒装再还原就是
I didn't received the manager's reply until nearly a month later
until nearly a month later,就是时间状语,
你硬要在插个when的状语从句,意思不就不对了吗