We all have a tendency to fake laugh，particularly when authority figures in our lives try to make a joke that just doesn't land．Though it might feel rude not to laugh when your in-laws or boss try to say something funny，pretending to do so might not be much better．It turns out，even if you think that your forced laughing sounds genuine，people are usually pretty good at separating truly spirited belly laughs from fake ones．But how can they possible know the difference？
   Well，when researchers at the University of California，Los Angeles studied the acoustic（听觉的）and perceptual（知觉的）differences between real and fake laughter，they found that some of the sounds associated with genuine laughter is "really hard to fake．" In their study，the researchers determined that subjects were only fooled by 37 percent of fake laughter．
   The most prominent factor distinguishing real laughter from fake laughter is duration -- or，more specifically，the number of breaths taken in in between sounds．Seeing as it takes more effort and concentration to fake a laugh as opposed to do it genuinely，people tend to pause more in between their "ha-ha's" when they're faking it．Evidently，that pausing is pretty noticeable．
   "A fake laugh is basically an imitation of a real laugh，but produced with a slightly different set of vocal muscles controlled by a different part of our brain，" Greg Bryant，the lead UCLA researcher on the study，explained． "The result is that there are subtle（微妙的）features of the laugh that sound like speech，and …people are unconsciously quite sensitive to them．"
   People have also proven to be emotionally sensitive to laughter as well． "Our rains are very sensitive to the social and emotional significance of laughter，" said Carolyn McGettigan，a scientist at Royal Holloway，University of London．
   McGettigan conducted a 2014 study that recorded participants' brain responses as they listened to the same people produce genuine laughter by watching funny videos，as opposed to fake laughter． "During our study，when participants heard a laugh that was posed，they activated regions of the brain associated with mentalizing in an attempt to understand the other person's emotional and mental state，" she said．
   So，while we may understand that certain social situations sometimes require fake laughter，most of the time，our instincts and emotional intelligence are just too smart to buy into them．
   According to McGettigan，that's a good thing． "Evolutionarily speaking，it's good to be able to detect if someone is authentically experiencing an emotion or if they're not，" she said． "Because you don't want to be fooled．"

（1）What do researchers at the University of California want to find out in this study？

A

A

A．What is the difference between a fake laugh and a real one．
B．Which part of the brain controls the sound of our laughter．
C．Why do people need to fake laugh when they don't want to．
D．How to laugh as genuinely as possible when you are faking it．
（2）Your forced laughing is more noticeable than you think，mainly because

B

B

．
A．you seem more concentrated when you laugh for real
B．you take more breaths when you try to fake a laugh
C．a fake laugh often happens after a sudden pause
D．a real laugh usually lasts longer than a fake one
（3）Which of the following is true according to Greg Bryant？

B

B

A．Real laughter is not at all controllable by our brain．
B．People may notice fake laughter without knowing why．
C．People use the same set of muscles to laugh and to speak．
D．Faking laugh shares the same techniques as making speech．
（4）What has Carolyn McGettigan's 2014 study proven？

D

D

A．Certain social situations may require us to fake a laugh．
B．Evolution has enabled us to recognize other's emotions．
C．By instincts，we are able to tell a person's mental state．
D．We can sense other's emotional state when they laugh．