The correct answer is A, direct fluorescent antibody assay (DFA).  Antigens of these parasites are released into the stool specimen.  If the stool was concentrated, the antigens would be poured off during the steps of the formalin-ethyl acetate concentration procedure.  Modified Kinyoun's acid-fast and trichrome stains detect Cryptosporidium sp. or G. intestinalis, respectively.