The evolutionary tree below illustrates the hypothesized relationships among the six kingdoms and the three domains.
Many biologists have suggested revising the kingdom Protista. One current problem with the protists, as shown in the figure, is that

A)protists are single-celled organisms and should be in a separate domain.
B)the cells of protists contain nuclei and organelles.
C)some protists, like the red and green algae, are more closely related to plants than to the other protists they are currently grouped with.
D)chlorophyll would need to evolve independently several times to account for the distribution of photosynthetic groups.