Select the most appropriate option lo fill in the blanks.

Cells also began living together, probably because certain benefits could be _________. Groups of cells might be able to feed more ________ or gain protection from simply being bigger. Living _________ , cells began to support the needs of the group by each cell doing a specific job.

The most appropriate option to fill in the blanks is Option A

So, the completed sentence would be:

Cells also began living together, probably because certain benefits could be obtained. Groups of cells might be able to feed more efficiently or gain protection from simply being bigger. Living collectively, cells began to support the needs of the group by each cell doing a specific job. 

This option makes the most sense in the context of cellular biology and the evolution of multicellular organisms.

Options B,C and D are not suitable because they contain words that do not match the blank in the given context.