A 12-year-old female is brought to the emergency department with meningitis and a history of swimming in a warm-water spring. Motile amoebae that measure 10μm in size are seen in the CSF and are most likely
a. Iodamoeba bütschlii trophozoites
b. Endolimax nana trophozoites
c. Dientamoeba fragilis trophozoites
d. Naegleria fowleri trophozoites
e. Giardia duodenalis trophozoites