Step 1: Understanding the Role
The question asks for the title of a political party official whose job is to ensure that members of their party attend parliamentary sessions and vote in accordance with the party's official policy. This is a key role in maintaining party discipline within a legislature.
Step 2: Defining the Terms
(A) Whip: In a parliamentary system, a Whip is an official of a political party whose task is to ensure party discipline in a legislature. This includes ensuring that members attend and vote as the party leadership desires. The term can also refer to the voting instruction itself issued by the party. This perfectly matches the description.
(B) Opposition leader: The leader of the largest political party that is not in government. They lead the opposition but do not enforce voting discipline for all parties.
(C) Agent: A general term for someone who acts on behalf of another, not specific to this parliamentary role.
(D) Representative: A general term for an elected member of the legislature.
Step 3: Final Answer
The party official responsible for enforcing party discipline and organizing voting is known as the Whip. Therefore, option (A) is the correct answer.