Final answer:
The television daypart with the highest rates and dominated by national advertisers is prime time, due to its high viewership in the evening hours.
Step-by-step explanation:
The television daypart that typically has the highest rates and is dominated by national advertisers is C. Prime time. This time slot is preferred by national advertisers because of its large audience reach, with the majority of viewers tuning in during the evening hours after work and before bedtime. During this period, networks produce a variety of popular shows in genres ranging from drama to comedy and reality television. The prime time segment provides advertisers with the opportunity to connect with a wide and engaged audience.