Many Parasitic Members of the Excavates Lack Plastids and Have

Many parasitic members of the excavates lack plastids and have highly reduced mitochondria. Which of the following statements explains these observations?

A) These parasites live in dark, low-oxygen conditions, and therefore it was adaptive to move all plastid and mitochondrial genes to the nucleus.
B) The original, eukaryotic ancestors of these parasites did not engulf prokaryotes.
C) These parasites live in dark, low-oxygen conditions and therefore loss of genes for plastids and mitochondria did not result in lower fitness.
D) In the future, natural selection will favor descendants that acquire new plastid genes from today's prokaryotes.