variant configuration

Hello SAP Gurus,

I have finish material as a Hardisk i have assigned 300 class for this i have created configuration profile in CU41. I have created BOM for this fert. In BOM 200GB & 100GB raw material is created for these two raw material class 200 is assigned also in BOM maintained as Class item. also one plastic case is also added in BOM item. Means in BOM there are three components 2 are configurable & one ROH. Now in CU50 if i select 200GB then in BOM explosion system should select 200GB & one plastic case. But its not happening I think it is problem of object dependency Now please tell me how to write a object dependency?

regards,

dev123.