Explanation:

- Option 1: Declaration

- This does not apply here. A declaration typically involves a formal statement or announcement and doesn't relate to the process of issuing summons.

- Option 2: Mandatory

- Mandatory actions are those required by law or rules. Section 91 does not mandate issuing summons automatically.

- Option 3: Discretionary

- This means that the authority to issue a summons under Section 91 rests on the discretion of the court or officer in charge. They decide based on the case’s requirements.

- Option 4: Either (a) or (c)

- This suggests a choice between declaration and discretionary, which isn’t correct as issuing summons under Section 91 isn't about declaration.