Is this sentence correctly using commas: polluted rivers, which can exist anywhere, are unsafe for swimming.

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.