有这样的用法：a good knowledge of 意为：通晓,对、、很了解,
常与 have/acquire/obtain/develop 等动词搭配
但是knowledge它本身是不可数的
common knowledge同样不可数
This is common knowledge,but a lot of people tend to ignore it.
It is common knowledge that fish can't live without water.
knowledge 可数吗? common knowledge （常识）可数吗? 造2个句,谢谢.