During speciation, when do two groups become recognized as separate species? a. when they look different. b. when they are separated by an isolation barrier. c. when they cannot interbreed. d. when they are both herbivores.

Which of the following would most directly interfere with sperm production? ingestion of a substance that mimicked inhibin interruption of sustentocytes' production of abp low sperm count use of synthetic steroids (testosterone)