People liked riding bicycles because bikes were not so expensive as horses这句话的同义句是什么?

题目

People liked riding bicycles because bikes were not so expensive as horses这句话的同义句是什么?
People liked riding bicycles because bikes were （ ）expensive（ ）horses

答案

People liked riding bikes because bikes were cheaper than horses.
你的补充
People liked riding bicycles because bikes were （less）expensive（than）horses