Meaning: 'Invested' means to allocate resources, such as time or money, towards a particular purpose, in this case, research.

Wrong options:

• conducted: 'Conducted' implies carrying out an action but does not convey the sense of resource allocation that 'invested' does.
• done: 'Done' is too vague and does not specifically indicate the effort or resources put into research.
• made: 'Made' is also too general and does not accurately reflect the context of dedicating time to research.

Correct answer: component

Explanation: The term 'component' accurately describes caves as a part of the natural environment, fitting both grammatically and contextually within the sentence structure.

Meaning: 'Component' refers to a part or element of a larger whole, indicating that caves are integral to the natural environment.

Wrong options:

• constituent: 'Constituent' refers to something that makes up a whole but is less commonly used in this context compared to 'component.'
• compartment: 'Compartment' suggests a separate section or division, which does not accurately represent the relationship of caves to the environment.
• complement: 'Complement' implies something that completes or goes well with something else, which does not fit the intended meaning here.

Correct answer: arouse

Explanation: The verb 'arouse' is appropriate as it conveys the idea of stimulating curiosity, fitting well with the context of the sentence about caves provoking interest.

Meaning: 'Arouse' means to evoke or awaken a feeling or response, in this case, curiosity about caves.

Wrong options:

• incite: 'Incite' typically has a negative connotation of provoking or stirring up, which does not align with the positive context of curiosity.
• tempt: 'Tempt' implies enticing someone to do something, which does not accurately reflect the nature of curiosity in this context.
• instigate: 'Instigate' suggests initiating something negative or undesirable, which is not the intended meaning regarding curiosity.

Correct answer: devoted

Explanation: The word 'devoted' fits grammatically and contextually as it indicates a significant commitment of research effort towards caves.

Meaning: 'Devoted' means to give a large part of one's time or resources to a particular activity, in this case, research on caves.

Wrong options:

• donated: 'Donated' implies giving something as a gift, which does not convey the ongoing effort and commitment implied by 'devoted.'
• bestowed: 'Bestowed' suggests giving something as a gift or honor, which does not fit the context of research effort.
• lavished: 'Lavished' implies excessive or extravagant giving, which does not accurately reflect the serious and focused nature of research effort.

Correct answer: agility

Explanation: The term 'agility' is appropriate as it refers to the physical ability required to navigate caves, fitting well within the context of the sentence.

Meaning: 'Agility' means the ability to move quickly and easily, which is necessary for cave exploration.

Wrong options:

• capacity: 'Capacity' refers to the maximum amount that something can contain, which does not relate to the physical ability needed for cave visits.
• properties: 'Properties' refers to characteristics or attributes, which does not convey the physical skill required for cave exploration.
• demands: 'Demands' suggests requirements or needs, but does not specifically address the physical ability needed to visit caves.

Correct answer: overlap

Explanation: The word 'overlap' fits well as it indicates a shared area or commonality between two fields, aligning with the context of the relationship between professional and amateur studies.

Meaning: 'Overlap' refers to a situation where two things share common elements or areas, indicating the connection between different types of cave studies.

Wrong options:

• underlay: 'Underlay' refers to something that lies beneath another, which does not fit the context of shared characteristics.
• startification: 'Startification' is not a standard term in this context and does not convey the intended meaning of shared areas.
• dependence: 'Dependence' implies reliance on something else, which does not accurately describe the relationship between professional and amateur studies.