How to rewrite in passive voice

"dogs make wonderful pets because they us stay happy and healthy"the topic sentence is "dogs make wonderful pets" i need writing a sentence that is unrelated to the topic and can be eliminated.

The greatest gift the sumerians gave the world was the invention of writing. the sumerians were wealthy people. they needed some way to keep track of what they owned. they began drawing pictures. they used a reed as a pen. they drew on soft pieces of clay. the soft clay was then dried in the sun. the tablet became a permanent record. later, the sumerian drawings changed into wedge-shaped symbols. this kind of writing is called cuneiform. by putting symbols together, the sumerians could write entire sentences.

Which statement best evaluates the author's use of pacing in the passage? a. the author's use of pacing is not effective, because the imagery and figurative language don't adequately describe either the cheetah or the gazelle. b. the author's use of pacing is effective, because the imagery and figurative language speed up the action, making the scene come alive for the reader. c. the author's use of pacing is effective, because the long, complex sentences the reader fully understand the power and beauty of nature. d. the author's use of pacing is not effective, because the long, complex sentences distract from the sense of stress and anxiety the passage should convey.