?Now researchers have found that humans produce a different odor （氣味） when under pressure-and dogs can sniff it out.While previous studies have suggested dogs might notice human emotions，possibly through smell，questions remained over whether they could detect stress and if this could be done through smell.
?Wilson，head of one research team，pointed the findings could prove useful when training service dogs，such as those that support people with PTSD （創(chuàng)傷后應(yīng)激障礙）. "They're often trained to look at someone either crouching down on the floor，crying out in fear，or starting to do self-injurious behaviors，" said Wilson.The latest study，she said，offers another potential clue.
?Wilson and colleagues trained four dogs to identify the container holding a particular breath and sweat sample，even when the containers included unused gauze （紗布），samples from another person，or samples from the same person taken at a different time of day.After the team is confident that the dogs understood the approach，they turned to collect breath and sweat samples collected from 36 people asked to count backwards from 9，000 in units of 17，and the participants reported feeling stressed.
?Later，the dogs were taught to pick out samples taken just after the task.The researchers then tested whether the dogs could do the same with samples taken from the same participant just before the task，when they were more relaxed.Each set of samples was shown to a single dog in 20 trials.
?The results reveal that the dogs chose the "stressed" sample in 675 out of the 720 trials.It was pretty amazing to see how smoothly the dogs act in telling people these two samples definitely different.

（1）Why did Wilson and colleagues do such an experiment？

D

D

A．To train service dogs for people with PTSD.
B．To help people understand how stressed they are .
C．To prove dogs could recognize human emotions
D．To confirm dogs can smell out stressed people.
（2）The service dogs will usually provide help when someone

A

A

.
A．hurts himself
B．lies on the bed
C．produces an odor
D．screams in excitement
（3）Which order does the experiment follow？

A

A

a.To train dogs to pick out the particular container.
b.To show each set of samples to a single dog in 20 trials.
c.To collect samples from participants when they are stressed out.
d.To ask participants to count backwards from 9，000 in units of 17.
A．a(chǎn)-d-c-b
B．a(chǎn)-c-d-b
C．c-a-d-b
D．c-a-b-d
（4）What's the author's attitude towards the finding？

B

B

A．Negative.
B．Positive.
C．Uncertain.
D．Neutral.