Meaning: 'Available' means that something is present and ready for use or access, indicating that the sources were there for students to utilize.

Wrong options:

• decipherable: 'Decipherable' means something that can be understood, which does not relate to the accessibility of sources in a library context.
• saleable: 'Saleable' refers to something that can be sold, which is irrelevant in the context of research materials being accessible in a library.
• conceivable: 'Conceivable' means something that can be imagined or thought of, which does not fit the context of physical sources being present in a library.

Correct answer: obtained

Explanation: The word 'obtained' is appropriate as it indicates the action of acquiring materials from other libraries, fitting both grammatically and contextually in the sentence.

Meaning: 'Obtained' means to get or acquire something, in this case, research materials from other libraries.

Wrong options:

• sustained: 'Sustained' means to maintain or support, which does not apply to the act of acquiring materials from libraries.
• refrained: 'Refrained' means to hold back or avoid, which contradicts the action of acquiring materials.
• guaranteed: 'Guaranteed' implies assurance or certainty, which does not fit the context of acquiring materials from other libraries.

Correct answer: associated

Explanation: The word 'associated' fits well as it indicates a connection with the information available on the Internet, aligning with the context of the sentence about the responsibility of researchers.

Meaning: 'Associated' means connected or related to something, in this case, the information linked to the Internet.

Wrong options:

• redeemed: 'Redeemed' means to recover or regain, which does not fit the context of information related to the Internet.
• disowned: 'Disowned' means to refuse to acknowledge or maintain a connection with, which is the opposite of what is intended in this context.
• dissociated: 'Dissociated' means to separate or disconnect, which contradicts the idea of being responsible for information related to the Internet.

Correct answer: within

Explanation: The word 'within' is suitable as it indicates something contained inside a specific area, which in this case refers to the library's walls, fitting grammatically and contextually.

Meaning: 'Within' means inside or contained by something, indicating that the information is located inside the library's walls.

Wrong options:

• off: 'Off' indicates separation or removal, which does not fit the context of being contained inside the library.
• besides: 'Besides' means in addition to, which does not convey the idea of containment within the library's walls.
• over: 'Over' implies a position above or across, which does not accurately describe the relationship of the information to the library's walls.