problem:

Green algae can occur as unicellular Chlamydomonas, colonial gonium, and multicellular Volvox.

Required:

Question: What can be said about these species and the evolution of multicellularity.
A) Although the cellularity of these genera suggests evolution from one species to another, morphological characters inside individual cells dispute this hypothesis.
B) Generic data suggesting that Volvox evolved from Gonium is our most convincing evidence that multicellular organisms evolved from unicellular organisms.
C) This hypothesis is one of many developed to explain the evolution of multicellularity.
D) Since none of these genera have ever existed at the same time, there is no data to sugggest they represent a model of evolution.
E) Each of these extant genera represents a modern cellular state that may have developed from a less complex ancestor.

I eliminated choices B and C, but can't further narrow this down. Please choose answer and explain why.