The correct option is B. A multi cellular organisms has many cells which carry out various function and which are organised into tissues, organs and organ system. A unicellular organism on the other hand has only one cell with different cell organelles. Thus, in unicellular organisms, it is the cell organelles that carry out different functions. <span />
B. organelles because organelles are structures in the cell for example the plasma membrane, nucleus, mitochondria, etc. which they all have their own functions to make life possible.
