Two weeks ago, a 5-year-old boy developed diarrhea, which has persisted to the present time despite dietary management. His stools have been watery, pale, and frothy. He has been afebrile. Microscopic examination of his stools is likely to show which of the following?
a) Giardia lamblia cysts
b) Enterobius vermicularis eggs
c) Cryptosporidium oocysts
d) Trichuris trichiura eggs