Meaning: 'Extremely' means to a very great degree; very.

Wrong options:

• compete: 'Compete' means to strive to win, which does not modify 'intelligent.'
• cited: 'Cited' means to refer to or mention, which does not fit here.
• herding: 'Herding' refers to managing livestock, not intelligence.

Correct answer: compete

Explanation: The verb 'compete' fits grammatically as it aligns with the subject 'they' and indicates the action they frequently engage in. It maintains the context of the sentence, which discusses their success in trials and sports.

Meaning: 'Compete' means to strive against others to achieve a goal or win.

Wrong options:

• extremely: 'Extremely' is an adverb, not a verb indicating action.
• cited: 'Cited' means to refer to, which does not fit here.
• herding: 'Herding' refers to managing livestock, not the action of participating in competitions.

Correct answer: cited

Explanation: The verb 'cited' fits grammatically as it indicates that they are frequently referred to or mentioned in discussions about intelligence. It aligns with the context of the sentence, which discusses their reputation.

Meaning: 'Cited' means to quote or refer to as an example or authority.

Wrong options:

• extremely: 'Extremely' is an adverb, not a verb.
• compete: 'Compete' is a verb but does not mean to refer to or mention.
• herding: 'Herding' refers to managing livestock, not to being referenced.

Correct answer: herding

Explanation: The gerund 'herding' fits grammatically as it describes the action of managing livestock, which is the traditional work of Border Collies. It maintains the context of the sentence, which discusses their employment.

Meaning: 'Herding' refers to the act of gathering and managing livestock.

Wrong options:

• extremely: 'Extremely' is an adverb, not a noun or verb.
• compete: 'Compete' is a verb, not the name of an action or occupation.
• cited: 'Cited' means to refer to, which does not fit here.