Final answer:
Option (D), The representation of Massachusetts in Congress has declined because its population growth has not kept pace with the growth of other states, leading to a redistribution of the fixed 435 House seats after each census.
Step-by-step explanation:
The representation of Massachusetts in Congress has declined despite an increase in population since 1970 because population growth in Massachusetts has not kept pace with the growth of other states. This is option D in the multiple-choice question provided. While Massachusetts' population has grown, other states have grown more rapidly, leading to a redistribution of House seats after each census.
The total number of House seats is capped at 435 due to the Apportionment Act of 1911, which is based on concerns about having a Congress that is too large and unwieldy, and the limitations in physical space to house an increasing number of representatives.
These legislative constraints impact how congressional districts are apportioned and reflect population shifts across the United States. States with faster population growth are allocated more congressional representatives, which may result in states with slower growth, such as Massachusetts, losing representatives even if their populations have increased.