Explanation:

- Option 1: A warrant of arrest must be a written order. This is essential for legal documentation and clarity.

- Option 2: A warrant is signed and issued by a Magistrate, giving it authority. It might also be sealed, depending on jurisdiction, to ensure authenticity.

- Option 3: The warrant is addressed to a police officer, specifying who is to execute the arrest. This ensures that the law is upheld by authorized persons.

- Option 4: All of the above. This option includes the necessity of a written format, proper issuance by a magistrate, and that it is directed towards a police officer.

Answer: Option 4 - all of the above.