Giardia Intestinalis Is an Intestinal Parasite of Humans and Other

Giardia intestinalis is an intestinal parasite of humans and other mammals that causes intestinal ailments in most people who ingest the cysts. Upon ingestion, each cyst releases two motile cells, called "trophozoites". These attach to the small intestine's lining via a ventral adhesive disk. The trophozoites anaerobically metabolise glucose from the host's intestinal contents to produce ATP. Reproduction is completely asexual, occurring by longitudinal binary fission of trophozoites, with each daughter cell receiving two haploid nuclei (n = 5) . A trophozoite will often encyst as it passes into the large intestine by secreting around itself a case that is resistant to cold, heat, and dehydration. Infection usually occurs by drinking untreated water that contains cysts.
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Giardia's mitosome can be said to be "doubly degenerate", because it is a degenerate type of ________, an organelle that is itself a degenerate form of ________.

A) nucleus; archaean
B) nucleus; bacterium
C) mitochondria; proteobacterium
D) mitochondria; spirochete