A、It urged people to improve the raising conditions. B、It helped people find the cure for bird flu. C、It made people to rethink

(19)As the human population has grown and become wealthier, the demand for high-quality animal protein has skyrocketed. For example, from 1990 to 2005, Asia alone added roughly one billion humans, but ten billion chickens, according to UN figures.(19)As a result, farmers are raising more animals in smaller spaces than in the past and in places that have not been used this way before, like in virgin forests or near dense urban environments. And this intensification is often taking place in poor conditions and with few regulations, according to animal disease expert Delia Grace from the International Livestock Research Institute. According to Grace, most of those novel diseases do not cause a great deal of harm. But some do. An example is the H5N1 avian influenza, also known as bird flu. More than 300 people have died from it to date, and the virus continues to circulate, killing one person in Cambodia this year. However, one good thing has come out of the experience.(20)"Avian influenza has been something which has made people certainly rethink the interdependence between animal health and human health," says Grace. She believes policymakers need to consider both human and animal health impacts because an estimated 700 million people in the developing world keep farm animals, which provide up to 40% of household income.(21)While animal diseases can pose a threat to human health, controlling them can pose an economic threat, if not done properly. Grace says as the pressure to intensify livestock production increases in response to growing demand, policymakers will need to carefully balance public health, animal
health and economic health.
19. Why do people raise more animals according to the passage?
20. What’s the positive effect of the experience that bird flu killed a lot of people?
21. What conclusion can we draw from the passage?