Naegleria fowleri is a free-living ________ that causes infection by ________.

A) amoeba / entering through the nose and burrowing into the brain
B) fungus / entering the lungs when contaminated soil is disturbed
C) flagellated protist / crossing the intestinal mucosa into the blood
D) protist / entering the vagina in women, the prostate and seminal vesicles of men, or the urethra of both males and females