(1) Once dry, Ts'ai Lun discovered that he had created a quality writing surface that was relatively easy to make and lightweight.
(2) He took the inner bark of a mulberry tree and bamboo fibers, mixes them with water, and pounded them with a wooden tool.
(3) He then poured this mixture onto a flat piece of coarsely woven cloth and let the water drain through, leaving only the fibers on the cloth.
(4) The person credited with inventing paper is a Chinese man named Ts'ai Lun.
Which sentence(s) contains an error in parallelism?