The navigators' lack of knowledge led to the loss of four ships and two thousand lives.

VOA: special.2010.07.14

And then, on the top of 3, we get another example: "In other words we've got to get on the ball, darling, what I'm saying, otherwise it'll be fluctuating and lack of true knowledge or crystallization of our plans."

然后，在第三页上面，又有一个例子：,换句话说我们必须去这个舞会，亲爱的，我是说，不然就会变得波动又缺少真知识,或使我们的计划结晶化“

耶鲁公开课 - 1945年后的美国小说课程节选

to express a lack of complete knowledge about the multitude of subjects.

它可以用来表达你对一些话题并不完全了解。

I don't know 课堂 - SpeakingMax英语口语达人

Dr.Huerta says many Latin and South American communities do not have mammography machines, and there is a general lack of knowledge about the disease.

VOA: standard.2010.02.02

but also very non-affrontively, express a lack of complete knowledge

又不冒犯地表达对某事不完全清楚，

I don't know 课堂 - SpeakingMax英语口语达人