A.I. Explanation:

Option 1: "show"

Explanation: The term 'show' does not fit the context of the sentence, as it does not convey the seriousness or depth of the situation described. The text discusses a significant event involving legal actions and political implications, which requires a term that reflects a thorough examination or inquiry.

Option 2: "investigation"

Explanation: The word 'investigation' is the correct choice as it aligns perfectly with the context of the text. The sentence refers to the FBI's involvement in examining the actions of Maria Butina, which is a clear indication of an investigation into her activities as a foreign agent.

Option 3: "campaign"

Explanation: The word 'campaign' suggests a planned series of activities aimed at achieving a specific goal, which does not accurately reflect the nature of the FBI's actions described in the text. The context is focused on legal scrutiny rather than a political campaign.

Option 4: "influence"

Explanation: While 'influence' relates to the actions of Maria Butina, it does not complete the sentence appropriately. The text is discussing the FBI's actions, which require a term that indicates a formal process of inquiry, making 'influence' an inadequate choice.