Meaning: 'Kinds' refers to different types or categories, indicating that knowledge can be classified in two ways.

Wrong options:

• ways: While 'ways' could imply methods, it does not specifically denote categories as 'kinds' does, making it less precise in this context.
• masses: The term 'masses' suggests large quantities rather than types, which does not fit the intended meaning of categorizing knowledge.
• volumes: 'Volumes' typically refers to physical books or quantities, not types of knowledge, thus it is not suitable in this context.

Correct answer: sources

Explanation: The word 'sources' is appropriate as it refers to origins of information, fitting the context of knowing where to find knowledge, and it is plural to match the sentence structure.

Meaning: 'Sources' means places or origins from which information can be obtained, emphasizing the importance of knowing where to look for knowledge.

Wrong options:

• races: 'Races' refers to groups of people or species, which is irrelevant in the context of knowledge and information.
• works: While 'works' could imply literary or artistic creations, it does not convey the idea of origins of information as effectively as 'sources'.
• things: The term 'things' is too vague and does not specifically relate to the concept of information origins, making it less suitable.

Correct answer: value

Explanation: The word 'value' fits well as it denotes the importance or usefulness of reference books, aligning with the context of discussing their significance in acquiring knowledge.

Meaning: 'Value' refers to the importance or worth of something, indicating how reference books contribute to knowledge acquisition.

Wrong options:

• reference: 'Reference' is a noun that does not fit grammatically in this context as it does not convey the intended meaning of importance.
• exist: 'Exist' is a verb that does not logically fit in the context of discussing the significance of reference books.
• easy: 'Easy' is an adjective that does not relate to the concept of importance or usefulness, making it an inappropriate choice.

Correct answer: intelligence

Explanation: The word 'intelligence' is suitable as it refers to the ability to acquire and apply knowledge and skills, fitting the context of using reference books effectively.

Meaning: 'Intelligence' refers to the capacity for learning, reasoning, and understanding, emphasizing the need for cognitive engagement with reference materials.

Wrong options:

• acceptance: 'Acceptance' implies agreement or approval, which does not relate to the active use of knowledge in this context.
• perception: 'Perception' refers to the way one interprets information, but it does not convey the active application of knowledge as 'intelligence' does.
• impact: 'Impact' suggests a strong effect or influence, which does not fit the context of actively using knowledge from reference books.

Correct answer: contributory

Explanation: The word 'contributory' is appropriate as it describes something that contributes to a particular outcome, fitting the context of reference books potentially leading to idleness.

Meaning: 'Contributory' means helping to cause or bring about something, indicating that reference books can play a role in promoting idleness if misused.

Wrong options:

• contribution: 'Contribution' is a noun that does not fit grammatically in this context, as the sentence requires an adjective to describe the nature of reference books.
• constant: 'Constant' implies something that is unchanging, which does not accurately describe the role of reference books in relation to idleness.
• conference: 'Conference' refers to a formal meeting, which is unrelated to the context of discussing the use of reference books.