Arrange sentences $A, B, C$ and $D$ between sentences $1$ and $6$, so as to form a logical sequence of six sentences.
1. So now let’s sum it up.
A. We can call this the material of knowledge.
B. According o Kant, there are two elements that contribute to man’s knowledge of the world.
C. The other is the internal conditions in man himself.
D. One is the external conditions that we cannot know of before we have perceived them through the series.
6. We can call this form of knowledge.