Meaning: 'Particularly' means 'especially' or 'specifically,' indicating that Goodall's work was especially significant in relation to chimpanzees.

Wrong options:

• closely: The adverb 'closely' implies proximity or attention but does not convey the emphasis needed in this context.
• faithfully: 'Faithfully' suggests loyalty or accuracy, which does not align with the intended meaning of emphasizing her focus on chimpanzees.
• perfectly: 'Perfectly' implies flawlessness, which is not the appropriate emphasis for her revolutionary work.

Correct answer: little

Explanation: The word 'little' is used to indicate a small amount or degree, which is appropriate here as it conveys that not much was known about chimpanzees before Goodall's research. It fits grammatically as an adjective modifying the noun 'was' and contextually reflects the limited knowledge prior to her work.

Meaning: 'Little' means 'not much' or 'a small amount,' indicating that there was minimal knowledge about chimpanzees' social lives and cognitive abilities.

Wrong options:

• few: 'Few' refers to countable nouns and implies a small number, which does not fit with the uncountable noun 'knowledge.'
• a few: Similar to 'few,' 'a few' suggests countable items and does not apply to the uncountable concept of knowledge.
• a little: 'A little' implies a small amount but is typically used with uncountable nouns in a more positive context, which does not align with the negative connotation of limited knowledge.

Correct answer: capable

Explanation: The word 'capable' indicates the ability to perform certain actions, which is fitting as it describes the skills of chimpanzees revealed by Goodall's research. It fits grammatically as an adjective describing 'chimps' and contextually highlights their abilities.

Meaning: 'Capable' means 'having the ability or qualities necessary to do something,' in this case, tool use and complex communication.

Wrong options:

• sufficient: 'Sufficient' means adequate or enough, which does not convey the active ability that 'capable' does.
• special: 'Special' implies uniqueness but does not directly relate to the abilities of chimpanzees in the context of the sentence.
• frequent: 'Frequent' refers to something occurring often, which is unrelated to the abilities of chimpanzees.

Correct answer: habitat

Explanation: The word 'habitat' refers to the natural environment in which an organism lives, making it the most suitable choice here. It fits grammatically as a noun that complements the verb 'observing' and contextually emphasizes the natural setting of Goodall's research.

Meaning: 'Habitat' means the natural home or environment of an animal, highlighting the importance of observing chimps in their own surroundings.

Wrong options:

• element: 'Element' refers to a component or part, which does not accurately describe the living environment of chimpanzees.
• input: 'Input' suggests contribution or data, which is not relevant to the context of observing animals in their environment.
• regime: 'Regime' typically refers to a system or planned way of doing things, which does not fit the context of natural living conditions.

Correct answer: highlighted

Explanation: The word 'highlighted' indicates that Goodall's work brought attention to the importance of ethical treatment, fitting grammatically as a verb in the past tense and contextually emphasizing the significance of her contributions.

Meaning: 'Highlighted' means to emphasize or make something stand out, in this case, the importance of ethical treatment of animals.

Wrong options:

• contacted: 'Contacted' implies reaching out to someone, which does not relate to emphasizing the importance of treatment.
• claimed: 'Claimed' suggests asserting something as a fact, which does not fit the context of emphasizing ethical treatment.
• comprised: 'Comprised' means to consist of or be made up of, which does not convey the action of emphasizing or bringing attention to an issue.