Filtering on a parameter value ??

HiNot sure why I'm stuck on this.. but I am I have a parameter called activestatus values are "A" for Active or "B" for "All"I want to filter the dataset by the field "Active" if the parameter value is "A" then get only "Active" field = "A" But... if the parameter is "B" then I want everything with no filtering... ThanksJoe