What kind of dx version use graphic engine of Guildwars?

Is it a full dx 8.1?
Main engine is 8.1 plus some adds of dx 9?
I believe that nightfall add some particular reflex and brightness features taken from dx9 effect? is it right?

I believe guildwars runs 9.0b? It can be made to run in 8.0/8.1 environments, but I thought it was 9.0b. O-o

When came prophecies i don't remember if dx 9 were out or not

DirectX 9.0c was already out when Prophecies was released.

DirectX 9.0c - August 2004
Prophecies - April 2005