Explanation:

- Section 87 of CrPC: This section allows a court to issue a warrant for the arrest of a person. This can be done when a summons is issued but is likely not to be effective.

- Option 1: In lieu of summon - A warrant can be issued instead of a summon if the court believes the summon may not ensure the person's presence.

- Option 2: In addition to summons - A warrant can also be issued alongside a summons if the court deems it necessary to secure attendance.

- Option 3: Both (a) & (b) - The section provides for issuing a warrant both in lieu of and in addition to a summons.

- Option 4: None of the above - This option is incorrect as Section 87 covers options 1 and 2.

Option 3: Both (a) & (b)