VOA慢速英语:研究人员：怎样让鸡快乐？

fake - adj. not true or real

welfare - n. the state of being happy, healthy, or successful; well-being

frequency - n. the fact or condition of happening often

organic - adj. grown or made without the use of artificial chemicals

track - v. to follow and find (someone or something) especially by looking at evidence

certify - v. to say officially that something or someone has met certain standards or requirements