What is the most likely reason that historic sites like the palace of westminster were built along the thames? a)the river was a place of recreation. b)the river offered people a beautiful view. eliminatec)the river needed to be defended from invaders. d)the river was the main mode of transportation.

I would argue that the right answer is the C: The river needed to be defended from invaders. The strategic site where the Royal Palace of Westminster (nowadays the home of the UK Parliament) is located, on the north bank of the River Thames, was originally a small island. This site has been historically used in order to build religious and royal buildings (a temple, a church, a monastery, a royal palace, and an abbey) and protect them from the invasions of the Danish and other peoples. For centuries, the Thames was much wider and shallower than it is today, and it helped to protect those who lived in those buildings, as well as the material property that they contained - works of art, the Royal treasure, and important documents, among others.  

thats exactly the right answer