Meaning: 'Discovered' means to find out something that was previously unknown or hidden, indicating that researchers have found new insights regarding voter turnout.

Wrong options:

• travelled: 'Travelled' implies movement from one place to another, which does not fit the context of finding information.
• jostled: 'Jostled' means to push or bump against someone, which is unrelated to the act of research or discovery.
• doubled: 'Doubled' refers to increasing something by twofold, which does not apply to the context of researchers finding information.

Correct answer: decision-making

Explanation: The term 'decision-making' is a noun that fits grammatically as it describes the process of making choices, which is the intended meaning in the context of improving voter turnout. It aligns well with the preceding phrase about results.

Meaning: 'Decision-making' refers to the cognitive process of selecting a course of action from multiple alternatives, relevant to the context of how fish choose their leaders.

Wrong options:

• vociferating: 'Vociferating' means to shout or complain loudly, which does not relate to the context of making decisions.
• symbolmaking: 'Symbolmaking' refers to the creation of symbols, which is not relevant to the context of voter turnout or decision processes.
• crepitating: 'Crepitating' means making a crackling sound, which is unrelated to the concept of making decisions.

Correct answer: stickleback

Explanation: The word 'stickleback' is a specific type of fish that fits grammatically as a noun and contextually as the subject of the study being discussed. It is the correct species being researched in relation to decision-making among fish.

Meaning: 'Stickleback' refers to a small fish known for its spiny dorsal fins, which is the focus of the study regarding leadership selection in fish.

Wrong options:

• bark: 'Bark' refers to the outer covering of a tree or the sound a dog makes, which is irrelevant to the context of fish.
• cask: 'Cask' is a barrel used for storing liquids, which does not relate to the subject of fish or research.
• disembark: 'Disembark' means to leave a ship or aircraft, which is not applicable in the context of fish or the study being discussed.

Correct answer: candidates

Explanation: The word 'candidates' fits grammatically as a plural noun, referring to the two mock leaders presented to the fish. It is contextually appropriate as it describes the options available for the fish to choose from.

Meaning: 'Candidates' are individuals being considered for a position or role, in this case, the leaders that the fish could follow in the experiment.

Wrong options:

• reallocates: 'Reallocates' is a verb meaning to distribute something again, which does not fit the context of presenting options to fish.
• validates: 'Validates' means to confirm or support something, which is not relevant to the context of choosing leaders.
• commentates: 'Commentates' is a verb meaning to provide commentary, which does not apply to the context of fish selecting leaders.

Correct answer: According

Explanation: The word 'According' fits grammatically as a preposition that introduces a source of information, aligning with the context of referencing the study. It is used to indicate that the following information is based on the findings of the study.

Meaning: 'According' means as stated by or in agreement with, indicating that the information that follows is derived from the study mentioned.

Wrong options:

• Crossing: 'Crossing' is a gerund or present participle that refers to moving from one side to another, which does not fit the context of referencing a study.
• Blowing: 'Blowing' is a verb that refers to the act of moving air, which is unrelated to the context of citing research findings.
• Torquing: 'Torquing' is a verb that refers to applying torque or twisting force, which does not apply to the context of discussing research results.