One reason the framers of the u. s. constitution favored a federal system over a unitary system is because they thought it would be cheaper. b. they wanted to keep states powerless. c. they wanted a limited national government. d. they thought it would collect more taxes.

C.they wanted a limited national government.

A unitary system posits all government power in a "unitary" or single place -- the central government.  A federal system has power shared between the national government and the states' governments.  The founding fathers of the United States wanted to avoid a system that looked like a monarchy, with all the powers centered on whomever was on the throne.  They wanted checks and balances of power, to keep tyranny in any form from arising.