Section B Directions：Fill in each blank with a proper word chosen from the box.Each word can only be used once.Note that there is one word more than you need.

A.feed B.crucial C.remarkable D.bond AB.jye.ai AC.captured AD.reinforcement BC.jye.ai BD.deliberate CD.jye.ai ABC.associate

Since its launch in September 2016 TikTok has taken the social media world by storm.Reaching half a billion active users worldwide in just under 2 years，it is the fastest app ever to reach that milestone.
 From the creator-first user experience to their flawlessly-executed global expansion，the Chinese video-sharing social network's meteoric rise has been nothing short of（1）

C

C

.TikTok's secret sauce，however，could well be found by looking into something far simpler than their algorithms（算法）and marketing tactics.Human evolution.
 Over the course of human history，as our ancestors began to live in larger and more complex social structures，the quality of our relationships became more（2）

B

B

to our survival.As the size of our networks increased around 10 million years ago，humans began developing a series of more advanced social behaviours that allowed us to connect larger groups and communities together.
 The first new behaviour was laughter.Laughter kicks our endorphins system into action，releasing feel-good hormones that relieve pain and increase pleasure.In doing so，we also create pathways that support the formation，（3）

AD

AD

，and maintenance of social bonds with other humans.
 Next came dancing and singing.Around 500，000 years ago，our social networks had dramatically increased in size again，tripling to approximately 150.At that point，humans needed even more sophisticated ways to（4）

D

D

with their social networks.It is then that scientists believe that music was 'invented' and that we first learned to sing and dance.
 Singing and dancing are intensely social and highly synchronised activities.They too release the same powerful endorphins as laughter.If you've ever been to a live music event or sung along to your national anthem in a major sporting event you will certainly be able to（5）

BC

BC

to the euphoria this brings.
 It is no wonder then that TikTok，a video-sharing app built entirely on people singing（or lip synching），dancing and laughter，has so quickly（6）

AC

AC

the minds of so many people.The app is in essence an infinite（7）

A

A

of endorphin-including content that triggers a strong sense of unity and belonging within us as we consume each video.
 Whether it was through（8）

BD

BD

design decisions or a happy coincidence，the app's creators have successfully（9）

CD

CD

their niche（商機）in an extremely competitive vertical through more than just smart technology or well-executed marketing.TikTok's rocket fuel has been derived from simply understanding and leveraging the human psychology that underpins the offline social world.
 In an era where questions are being asked of whether incumbent social platforms are really connecting us，perhaps we will see（10）

AB

AB

opportunities for social apps to do much better by bringing more of our offline social behaviours online.With COVID-19 highlighting the importance of offline social interaction and human connection，the market is certainly more ripe than ever for further disruption.