Enthuware

Why is the answer saying that both the clients and the business delegate have to know what technology they will use to communicate ? Isn't the goal of a business delegate to hide from the clients the fact that the business services can come from different registries and make that transparent ?
Should a client really know that the business service its asking is located on a RMI Registry or other ?

Yes, business delegate can use any technology it wants internally to implement its logic. However, the option is talking about the technology used to communicate between the client and the business delegate. Both have to know that technology to be able to communicate with each other.
HTH,
Paul.