Answer:
The correct answer to the question: Which factor contributed most to the changes shown in the table, would be, indeed, B: The increase in birthrate.
Step-by-step explanation:
The reason for this being the correct answer is that the table shows the growth in number of representatives from the House of Representatives throughout the years 1960, 1970 and 1980 from the different states: Colorado, New York, Pennsylvania and Texas. This increase in numbers directly relates to the growth in population numbers for each of these states, given that in the House, the number of representatives will depend on the population count.