Answer:
The correct answer is B- cells specialize and cooperate
Step-by-step explanation:
A unicellular organism is made up of single-cell and this single cell performs all the function to make the organism live and multicellular organisms are made up of multiple cells that are organized and each cells are specialized for performing a particular function and each cell in a structure cooperated each other to support the organism.
Therefore for a cell or group of cells to evolve in a multicellular organism, the cells must be specialized to perform different functions and should cooperate each other to perform these functions.
Volvox can live in colonies which can have 50,000 cells but they are unicellular because each cell is not specialized to perform different function.