ok, I see what you mean... choose cannot be used with a single variable like that, so you will have to use tokenCount and tokenAt.
set the Sp_Data.BChoice to the list of possible objects "Sp_B1,Sp_B2,Sp_B3..."
then: create object(tokenat(SP_Data.BChoice,floor(random(tokencount(SP_Data.BChoice,","))),","))
what that does is count how many choices there are:
HowMany = tokencount(SP_Data.BChoice,",")
then randomly chooses one of them:
WhichOne = floor(random(HowMany))
and then extracts the text of the one choosen: