Explanation:

- Section 160 of the Criminal Procedure Code (Cr PC) empowers a police officer to require the attendance of a person who is acquainted with the facts of the case.

- This section is usually invoked during investigations.

- Option 1: Notice by Telephone

- Phone notifications are typically informal and not addressed in Section 160 of Cr PC.

- Option 2: Notice in Writing

- ? Section 160 predominantly mandates written notice for official summons.

- Ensures a formal record and clarity regarding the call.

- Option 3: Either (a) or (b)

- Mixing forms isn't generally recognized for formal attendance requests in legal terms.

- Option 4: Both (a) and (b)

- Redundant and unnecessary in legal summons which favors writing.

Correct Answer: Option 2 - notice in writing