Meaning: 'Hallmarks' means distinctive features or traits that signify something's quality or nature, in this case, sharing as a key trait of humanity.

Wrong options:

• nauseous: 'Nauseous' describes a feeling of sickness and does not fit grammatically or contextually as it is an adjective, not a noun.
• enormous: 'Enormous' is an adjective meaning very large, which does not fit as it does not describe a characteristic of sharing.
• notice: 'Notice' is a noun referring to an announcement or warning, which does not align with the context of describing a trait.

Correct answer: behaviors

Explanation: The word 'behaviors' is a plural noun that fits grammatically after 'human,' indicating the various actions or conduct of humans. It is contextually appropriate as it relates to the act of sharing.

Meaning: 'Behaviors' refers to the actions or reactions of individuals or groups, particularly in response to external stimuli, in this case, sharing.

Wrong options:

• manners: 'Manners' refers to social conduct or etiquette, which is too narrow and does not encompass the broader concept of sharing as a behavior.
• expropriators: 'Expropriators' refers to those who take property for public use, which is unrelated to the context of sharing and does not fit grammatically.
• tabors: 'Tabors' refers to a type of drum, which is irrelevant in this context and does not fit grammatically.

Correct answer: strangers

Explanation: The word 'strangers' is a plural noun that fits grammatically and contextually, as it indicates individuals whom the bonobos do not know, aligning with the surprising behavior of sharing with them first.

Meaning: 'Strangers' refers to people or beings that one does not know, which is relevant to the context of bonobos sharing food.

Wrong options:

• whalers: 'Whalers' refers to those who hunt whales, which is unrelated to the context of sharing and does not fit grammatically.
• azaleas: 'Azaleas' are flowering plants, which are irrelevant in this context and do not fit grammatically.
• hazers: 'Hazers' refers to those who intimidate or bully, which does not fit the context of sharing and is not relevant.

Correct answer: experiment

Explanation: The word 'experiment' is a noun that fits grammatically and contextually, as it describes the scientific study conducted to test bonobo sharing behavior.

Meaning: 'Experiment' refers to a scientific procedure undertaken to make a discovery or test a hypothesis, which is relevant to the context of the study.

Wrong options:

• carefullest: 'Carefullest' is a superlative form of 'careful,' which does not fit grammatically as it does not describe a type of study.
• deliberate: 'Deliberate' is an adjective meaning intentional, which does not fit grammatically as it does not describe a noun in this context.
• deficit: 'Deficit' refers to a lack or shortfall, which is unrelated to the context of conducting a study.

Correct answer: fourteen

Explanation: The word 'fourteen' is a numeral that fits grammatically as it quantifies the number of apes involved in the experiment, aligning with the context of the study.

Meaning: 'Fourteen' is the number 14, indicating the quantity of bonobos that participated in the experiment.

Wrong options:

• theophylline: 'Theophylline' is a drug used in treating respiratory diseases, which is irrelevant in this context and does not fit grammatically.
• wolverine: 'Wolverine' refers to a type of animal, which does not fit the context of counting apes in the experiment.
• careen: 'Careen' means to tilt or lean, which is unrelated to the context of counting participants.

Correct answer: scientists

Explanation: The word 'scientists' is a plural noun that fits grammatically and contextually, as it refers to the researchers conducting the study on bonobo sharing behavior.

Meaning: 'Scientists' are individuals who conduct scientific research and experiments, relevant to the context of the study being discussed.

Wrong options:

• mileages: 'Mileages' refers to the distance traveled or the efficiency of fuel consumption, which is irrelevant in this context and does not fit grammatically.
• hybridise: 'Hybridise' is a verb meaning to mix different species, which does not fit grammatically or contextually in this sentence.
• semifinalists: 'Semifinalists' refers to participants in a competition who reach the semifinals, which is unrelated to the context of scientific research.