Final answer:
True. The major networks (ABC, CBS, and NBC) have lost a significant portion of their viewer base due to the number and diversity of cable offerings.
Step-by-step explanation:
True. Right up through the 1970s, U.S. television was dominated by three major networks (ABC, CBS, and NBC) that competed for ratings and advertising dollars. However, with the number and diversity of cable offerings, these major networks have lost a significant portion of their viewer base. Cable television has provided viewers with more options and specialized channels, leading to a decline in the audience for the major networks.