Dogs can be worried and pessimistic just like people, researchers report in a new study in Current Biology. And they aren't talking about basset hounds  : those dogs just look as if they expect the worst. What the scientists say is that dogs that exhibit anxiety when left home alone by their owners may have bigger problems -- they may be in a permanent bad mood. This pessimistic outlook may not otherwise be easily apparent in a dog's other characteristics, like running speed or learning ability, the study reports. Dogs are similar to humans in the role that emotional state plays in decision making, said Michael Mendel, a veterinary scientist at the University of Bristol and the study's lead author. The study's researchers looked at 24 dogs in shelters in Britain. They placed the dogs in isolated settings and observed their reactions -- many barked, jumped on furniture and scratched at the door. Then they placed bowls in two rooms. One bowl contained food, while another was empty. After training the dogs to understand that bowls can sometimes be empty, and sometimes full, they began to place bowls in ambiguous locations. Dogs that quickly raced to the locations were more optimistic, and in search of food. Those that did not were deemed pessimistic. The more separation anxiety a dog expressed while in isolation, the more likely the dog was to have a pessimistic reaction, the researchers found. The study carries an important message for dog owners, Dr. Mendel said. Dogs that express serious anxiety when alone may need treatment, as it could be a sign of unhappiness and instability. In the study, many dogs barked, jumped and scratched because    _   .
they couldn't find the bowl with food in it they were left alone they needed to be treated they wanted to be active and optimistic
Question: Dogs can be worried and pessimistic just like people, researchers report in a new study in Current Biology. And they aren't talking about basset hounds  : those dogs just look as if they expect the worst. What the scientists say is that dogs that exhibit anxiety when left home alone by their owners may have bigger problems -- they may be in a permanent bad mood. This pessimistic outlook may not otherwise be easily apparent in a dog's other characteristics, like running speed or learning ability, the study reports. Dogs are similar to humans in the role that emotional state plays in decision making, said Michael Mendel, a veterinary scientist at the University of Bristol and the study's lead author. The study's researchers looked at 24 dogs in shelters in Britain. They placed the dogs in isolated settings and observed their reactions -- many barked, jumped on furniture and scratched at the door. Then they placed bowls in two rooms. One bowl contained food, while another was empty. After training the dogs to understand that bowls can sometimes be empty, and sometimes full, they began to place bowls in ambiguous locations. Dogs that quickly raced to the locations were more optimistic, and in search of food. Those that did not were deemed pessimistic. The more separation anxiety a dog expressed while in isolation, the more likely the dog was to have a pessimistic reaction, the researchers found. The study carries an important message for dog owners, Dr. Mendel said. Dogs that express serious anxiety when alone may need treatment, as it could be a sign of unhappiness and instability. In the study, many dogs barked, jumped and scratched because    _   .
A. they couldn't find the bowl with food in it
B. they were left alone
C. they needed to be treated
D. they wanted to be active and optimistic
Answer: