There is a large outbreak of diarrhea in daycare centers throughout a city.  Several of the local hospitals have performed formalin-ethyl acetate concentrations on fecal specimens from the sick children.  Because these hospitals rarely see parasites, they request that the stool concentrates be forwarded to a reference lab for identification.  Both Giardia intestinalis and Cryptosporidium sp. would be suspect in this outbreak.  Which of the following diagnostic methods would be appropriate for detection of BOTH G. intestinalis or Cryptosporidium sp. from the stool concentrates?

(a) Direct fluorescent antibody assay (DFA)
(b) Enzyme immunoassay (EIA)
(c) Trichrome permanent stained slide
(d) Modified Kinyoun's acid-fast stain