A
Below is a question with multiple-choice answers. Choose the correct option based on your reasoning.

### Question:
Which sentence best describes the organization of the heart?

### Choices:
A. The heart is an organ made up of different types of tissues, each of which has different types of cells.
B. The heart is a tissue made up of different types of organs, each of which has different types of cells.
C. The heart is a system made up of one type of tissue and identical cells.
D. The heart is a tissue made up of one type of organ and identical cells.

### Answer:
