Answer :
A possible reason for the transition of algae from unicellularity to multicellularity would be the evolution of multicellularity allowed algae to develop traits that keep them close to the land and thus a source of nutrients. The correct answer between all the choices given is the last choice. I am hoping that this answer has satisfied your query and it will be able to help you in your endeavor, and if you would like, feel free to ask another question.
Answer:
C- the evolution of multicellularity allowed algae to develop traits that keep them close to the land and thus a source of nutrients .