Meaning: 'String' in this context refers to a series or sequence of related events or items.

Wrong options:

• decade: The word 'decade' refers to a period of ten years, which does not fit the context of describing a series of reports.
• reasons: While 'reasons' is relevant to the context, it does not grammatically fit as it does not describe a series or sequence.
• prices: 'Prices' refers to monetary values and does not relate to the concept of a series of reports.
• effects: 'Effects' refers to outcomes or results, which does not fit the context of a series of reports.
• momentum: 'Momentum' refers to the force or speed of movement, which does not describe a series of reports.

Correct answer: reasons

Explanation: The term 'reasons' fits grammatically as it serves as the subject of the clause that explains the variability in the reports. It aligns with the context of discussing the factors contributing to the disappointing results.

Meaning: 'Reasons' refers to the explanations or justifications for the disappointing reports.

Wrong options:

• decade: 'Decade' does not fit as it refers to a time period rather than an explanation for the reports.
• prices: 'Prices' does not fit as it refers to monetary values, not explanations for the reports.
• effects: 'Effects' refers to outcomes rather than the reasons behind the reports, making it contextually inappropriate.
• momentum: 'Momentum' refers to the force of movement and does not relate to the explanations for the reports.
• string: 'String' refers to a series and does not fit as an explanation for the reports.

Correct answer: prices

Explanation: The word 'prices' fits grammatically as it serves as the object of the clause discussing the factors affecting the reports. It is contextually relevant as it refers to the declining costs associated with online advertising.

Meaning: 'Prices' refers to the monetary values assigned to goods or services, in this case, online ads.

Wrong options:

• decade: 'Decade' does not fit as it refers to a time period rather than a monetary value.
• reasons: 'Reasons' does not fit as it refers to explanations, not monetary values.
• effects: 'Effects' refers to outcomes rather than monetary values, making it contextually inappropriate.
• momentum: 'Momentum' refers to the force of movement and does not relate to monetary values.
• string: 'String' refers to a series and does not fit as a monetary value.

Correct answer: momentum

Explanation: The term 'momentum' fits grammatically as it serves as the object of the clause discussing the challenges faced by the companies. It is contextually relevant as it refers to the ongoing progress or growth that is becoming harder to maintain.

Meaning: 'Momentum' refers to the force or speed of movement, particularly in the context of maintaining growth or progress.

Wrong options:

• decade: 'Decade' does not fit as it refers to a time period rather than a concept of ongoing progress.
• reasons: 'Reasons' does not fit as it refers to explanations, not the concept of maintaining growth.
• prices: 'Prices' refers to monetary values and does not relate to the concept of ongoing progress.
• effects: 'Effects' refers to outcomes rather than the concept of maintaining growth, making it contextually inappropriate.
• string: 'String' refers to a series and does not fit as a concept of ongoing progress.