The correct answer is C) the river needed to be defended from invaders.
The MOST LIKELY reason that historic sites like the Palace of Westminster were built along the Thames was that the river needed to be defended from invaders.
The beautiful and iconic building of the British Parliament is also known as the Westminister started to be constructed after the fire of 1834 that destroyed the old Westminister Palace. Charles Barry and A. W. N. Pugin designed the beautiful Gothic style in 1837 with the famous Big Ben tower. Being next to the Thames River helped the palace to defend against invasions,