How to explain why Renchen sat in the library that day in the eight characters?

Renchen Day: Renchen, water also. Chen, the reservoir is also. So, in the morning, I sit in the morning and sit in the library.

Ku: Chen, Xu, Chou, Wei, Si and Wu belong to the earth. There are four libraries:

Chen, reservoir; Hey, fire station; Ugly, vault; No, the wooden library.