Final answer:
A congressional district most likely changes shape because of gerrymandering, where the controlling party in the state legislature draws districts to their advantage.
Step-by-step explanation:
The most likely explanation for a congressional district to change shape is b) The district was drawn to the advantage of the party in control of the state legislature. This process, known as gerrymandering, occurs when the political party in power during the redistricting process, which follows the census every ten years, draws the district lines in a way that favors its candidates. This manipulation of district boundaries to favor one party can also occur when there is a gain or loss of seats in the House or to ensure equal population distribution within the districts, accounting for shifts in the population.