knowledge是可数还是不可数

There is a lack of knowledge about the tax system.

大家对税制缺乏了解。

For years we had little knowledge of what life was like inside China.

以往很多年我们对于中国国内的'生活情况所知甚少。

He never made a will, to the best of my knowledge.

据我所知，他从未立过遗嘱。

She has acquired a good knowledge of English.

她英语已经学得很好。

Our knowledge of the disease has advanced considerably over recent years.

近年来我们对这种疾病的了解深入多了。