How can we measure animals' emotions? A new study of animal's emotions suggests that, as in humans, emotions can tell animals about how dangerous their world is, and guide the choices that they make. The article of the study by Bristol University's professor Mike Mendl was published online. An animal living in an environment where it is often threatened by predators will develop a negative emotion or "mood", such as anxiety. However, one in an environment with plenty of opportunities to get resources for survival will be in a more positive mood state. The researchers say that these emotional states not only show the animal's experiences, but also help it decide how to make choices, especially in unclear situations. This could have good or bad results. An animal in a negative mood state will make a safety-first with a "pessimistic" response to an unclear event. For example, it considers a noise in the grass as a signal of the predator. At the same time, an animal in a positive mood state will benefit from a more "optimistic" response. It considers the noise as a signal of prey . Professor Mike Mendl, head of the Animal Welfare and Behavior Research Group at Bristol University's School of Clinical Veterinary Science said, " We can use "optimistic" or "pessimistic"decision-making as a symbol of an animal's emotional state. Recent studies by our group and others suggest that this is a _ new approach to studying a variety of animal species." "Public interest in animal welfare remains high, with widespread concern about the way in which animals are treated, used and included in society. To understand how animals should be treated, we need to better understand their emotional lives," Mike Mendl said. The researchers believe Mike Mendl's study can help them to better understand and assess an animal's emotions. We can infer from the passage that   _  .
the animals with positive emotions live longer there is no way to assess an animal's emotions few people care about animal welfare nowadays the environment can influence animal's emotions
Question: How can we measure animals' emotions? A new study of animal's emotions suggests that, as in humans, emotions can tell animals about how dangerous their world is, and guide the choices that they make. The article of the study by Bristol University's professor Mike Mendl was published online. An animal living in an environment where it is often threatened by predators will develop a negative emotion or "mood", such as anxiety. However, one in an environment with plenty of opportunities to get resources for survival will be in a more positive mood state. The researchers say that these emotional states not only show the animal's experiences, but also help it decide how to make choices, especially in unclear situations. This could have good or bad results. An animal in a negative mood state will make a safety-first with a "pessimistic" response to an unclear event. For example, it considers a noise in the grass as a signal of the predator. At the same time, an animal in a positive mood state will benefit from a more "optimistic" response. It considers the noise as a signal of prey . Professor Mike Mendl, head of the Animal Welfare and Behavior Research Group at Bristol University's School of Clinical Veterinary Science said, " We can use "optimistic" or "pessimistic"decision-making as a symbol of an animal's emotional state. Recent studies by our group and others suggest that this is a _ new approach to studying a variety of animal species." "Public interest in animal welfare remains high, with widespread concern about the way in which animals are treated, used and included in society. To understand how animals should be treated, we need to better understand their emotional lives," Mike Mendl said. The researchers believe Mike Mendl's study can help them to better understand and assess an animal's emotions. We can infer from the passage that   _  .
A. the animals with positive emotions live longer
B. there is no way to assess an animal's emotions
C. few people care about animal welfare nowadays
D. the environment can influence animal's emotions
Answer: