Meaning: 'Stressed' means experiencing mental or emotional strain, which is relevant here as it describes the potential impact on the rodents' well-being and research outcomes.

Wrong options:

• unrest: Unrest refers to a state of dissatisfaction or agitation, which does not fit grammatically or contextually as it does not describe the condition of the rodents directly.
• confessed: Confessed is the past tense of confess, meaning to admit something, which is irrelevant in this context as it does not relate to the state of the rodents.
• bread: Bread is a noun referring to a type of food, which does not fit the context of describing the emotional state of the rodents.

Correct answer: response

Explanation: The word 'response' is a noun that fits grammatically as it refers to the reaction of the mice to pain. It is contextually appropriate as it describes the observed behavior of the rodents in the study.

Meaning: 'Response' means a reaction to something, in this case, the pain experienced by the mice when an irritant was introduced.

Wrong options:

• sacs: Sacs are containers or pouches, which do not relate to the context of pain or reaction, making it grammatically and contextually incorrect.
• births: Births refer to the act of giving birth, which is unrelated to the context of pain response in the study.
• massage: Massage refers to the act of rubbing or kneading the body, which does not fit the context of a pain reaction.

Correct answer: injected

Explanation: The word 'injected' is the past participle of the verb 'inject,' which fits grammatically as it describes the action taken by the researchers. It is contextually relevant as it indicates the method used to introduce the irritant to the rodents.

Meaning: 'Injected' means to introduce a substance into the body using a syringe or similar device, which is the method used in the experiment.

Wrong options:

• sprinkled: Sprinkled implies scattering or scattering lightly, which does not accurately describe the method of introducing an irritant in a controlled experiment.
• nettled: Nettled means to irritate or annoy, which does not fit grammatically as it does not describe an action taken on the rodents.
• ingested: Ingested means to take in food or drink, which is not applicable here as the irritant was not consumed but rather introduced through injection.

Correct answer: odoriferous

Explanation: The word 'odoriferous' is an adjective that fits grammatically as it describes the T-shirt's characteristic of having a smell. It is contextually relevant as it relates to the scent that affects the rodents' behavior.

Meaning: 'Odoriferous' means having a strong smell, which is pertinent as it describes the scent of the male researcher's T-shirt that influenced the rodents' reactions.

Wrong options:

• deaconess: Deaconess refers to a female deacon in a church, which is irrelevant in this context and does not fit grammatically or contextually.
• creaminess: Creaminess describes a texture or quality of being creamy, which does not relate to the context of smell or odor.
• facetiousness: Facetiousness refers to treating serious issues with deliberately inappropriate humor, which does not fit the context of describing a physical characteristic.

Correct answer: reaction

Explanation: The word 'reaction' is a noun that fits grammatically as it describes the response of the rodents to the presence of female observers. It is contextually appropriate as it refers to the behavioral change observed in the study.

Meaning: 'Reaction' means a response to a stimulus, which in this case refers to how the rodents behaved when different observers were present.

Wrong options:

• compunction: Compunction refers to a feeling of guilt or moral scruple, which does not fit the context of the rodents' behavior in response to observers.
• version: Version refers to a particular form or variant of something, which is unrelated to the context of animal behavior.
• handgun: Handgun is a type of firearm, which is irrelevant and does not relate to the context of the study on rodent behavior.

Correct answer: temperature

Explanation: The word 'temperature' is a noun that fits grammatically as it refers to the physical condition of the rodents' bodies. It is contextually relevant as it relates to the physiological response to stress.

Meaning: 'Temperature' refers to the degree of heat present in the body, which is significant in understanding the stress response in rodents.

Wrong options:

• bickerer: Bickerer refers to a person who argues or quarrels, which is irrelevant in this context and does not fit grammatically or contextually.
• stepmother: Stepmother refers to a woman who is married to one's father after the divorce or death of one's mother, which does not relate to the context of stress or temperature.
• temperate: Temperate describes a moderate climate or behavior, which does not fit the context of measuring a physical condition like temperature.