Meaning: 'Delighted' means feeling or showing great pleasure or satisfaction.

Wrong options:

• popular: The word 'popular' is an adjective that describes something widely liked or accepted, which does not convey the emotional response of writers finding good sources.
• credibility: 'Credibility' is a noun that refers to the quality of being trusted or believed, which does not fit grammatically as it cannot describe the state of writers.
• integration: 'Integration' is a noun that refers to the process of combining things, which does not fit as it does not describe an emotional state.
• performance: 'Performance' is a noun that refers to how well someone does something, which does not relate to the emotional response of writers.
• capacity: 'Capacity' is a noun that refers to the maximum amount that something can contain or produce, which does not fit the context of emotional response.

Correct answer: integration

Explanation: The term 'integration' is a noun that refers to the process of combining sources into an argument. It fits grammatically as it follows the verb 'adds' and is essential to the context of discussing how sources enhance writing.

Meaning: 'Integration' means the act of combining or coordinating different elements into a whole.

Wrong options:

• delighted: 'Delighted' is an adjective that describes an emotional state, which does not fit as it cannot describe the action of combining sources.
• credibility: 'Credibility' is a noun that refers to the quality of being trusted, which does not fit as it does not describe the action of using sources.
• popular: 'Popular' is an adjective that describes something widely liked, which does not relate to the process of combining sources.
• performance: 'Performance' is a noun that refers to how well something is done, which does not fit the context of integrating sources.
• capacity: 'Capacity' is a noun that refers to the maximum amount something can hold, which does not fit the context of combining sources.

Correct answer: credibility

Explanation: The word 'credibility' is a noun that refers to the quality of being trusted or believed. It fits grammatically as it follows the verb 'builds' and is relevant to the context of enhancing the argument and the writer's trustworthiness.

Meaning: 'Credibility' means the quality of being convincing or believable.

Wrong options:

• delighted: 'Delighted' is an adjective that describes an emotional state, which does not fit as it cannot describe the quality of an argument.
• integration: 'Integration' is a noun that refers to the process of combining sources, which does not fit as it does not describe the quality of trustworthiness.
• popular: 'Popular' is an adjective that describes something widely liked, which does not relate to the quality of an argument.
• performance: 'Performance' is a noun that refers to how well something is done, which does not fit the context of trustworthiness.
• capacity: 'Capacity' is a noun that refers to the maximum amount something can hold, which does not fit the context of an argument's quality.