Asp.Net Dependency question

I have a dll, call it dllA and dllA references dllB. When I put dllA in the bin folder of my asp.net application, and call a method in dllA that references dllB, the asp.net application throws an error saying can't find dllB. I have to add dllB to the asp.net bin folder as well. My question is why, if I'm only refer开发者_如何学Pythonencing classes from dllB from dllA, do I have to add dllB in the bin folder along with dllA?

If you reference in dllA from dllB, how is dllA going to call that reference without a copy of dllB?

Every assembly that has code that is excuted on your page either needs to be in the bin folder for your asp.net app or in the GAC.