Historically, the Protists Were Classified in "Kingdom Protista

Historically, the protists were classified in "kingdom Protista." Recently, however, the protists were reclassified into "supergroups." What was the reason for this reclassification?

A) There were too many protist species to fit into a single kingdom.
B) Scientists decided to reclassify protists based on their nutritional mode. For example, all the photosynthesizers were placed together into one supergroup.
C) Scientists reclassified protists based on how many cells the organism contains. For example, there is a supergroup for one-celled organisms, a supergroup for two-celled organisms, etc.
D) New DNA evidence suggests that not all protists share a common ancestor and therefore their classification needed to be reorganized.