Which sentence best describes the organization of the heart? Available choices:
I. The heart is an organ made up of different types of tissues, each of which has different types of cells.;
II. The heart is a tissue made up of different types of organs, each of which has different types of cells.;
III. The heart is a system made up of one type of tissue and identical cells.;
IV. The heart is a tissue made up of one type of organ and identical cells.;
Your answer: