Please choose the correct answer to the question: Which sentence best describes the organization of the heart?

Answer1: The heart is an organ made up of different types of tissues, each of which has different types of cells. Answer2: The heart is a tissue made up of different types of organs, each of which has different types of cells. Answer3: The heart is a system made up of one type of tissue and identical cells. Answer4: The heart is a tissue made up of one type of organ and identical cells.

Answer format: answer1/answer2/answer3/answer4
Answer: answer1