My wallet is missing,but I really don’t know _________it disappeared.A.when it was that B.it was when that C.when was it that D.it was when请详细说明选择理由,

B强调

A.
know后面的宾语从句需要由when引导，由于不是独立疑问句所以从句中的主谓it was不需颠倒。

B it is/was ...that 是强调句型,可以省略
宾语从句用陈述句语气,所以B
我的钱包掉了,我真不知道它到底是什么时候丢的.

楼上不对, 应该是 A
先说强调句. 强调句的陈述句如下:
It was yesterday that it disappeared.
问句就是
When was it that it disappeared? 强调式的疑问句
比较强调式的疑问句和非强调式的疑问句:
When did it disappear? 非强调式的疑问句
那么变成从句的时候, 语序要变过来:
I don't know when it was that it disappeared --> 所以答案是 A
不管是 'it was' 还是 'was it', when 都要在出现在前面.
类似的句子还有:
I don't remember when it was that they broke into my house. 我不记得他们什么时候偷偷到我家里来的.
I don't know when it was that I first saw that movie. 我不知道我第一次是什么看的这个电影.
清楚了吗?