1.They are enjoying themselves
= They are having a good time.
2.Although he is young,he knows a lot about science
= He is young,but he knows a lot about science.
3.The telephone enables you to talk to people in the other cities
= The telephone makes you able to talk to people in the other cities
4.Qingdao is konwn for his beers and beautiful beaches
= Qingdao is famous for his beers and beautiful beaches
5.What are you planning to do this evening
= What are you going to do this evening
6.The best-known plants in Shenzhen are azaleas
= The most famous plants in Shenzhen are azaleas
7.This book belongs to my sister
= This book is my sister's.
8.Trees are communicating with one another
= Trees are communicating with each other.
=Trees are getting in touch with one another.
9.Trees can release oxygen
= Trees can give off / 或：set free oxygen
10.My father warns me not to swim in the river
= My father warns me that I mustn't swim in the river
11.Trees provide shelter and food for people
= Trees provide people with shelter and food.
12.Look out /watch out!Don’t play with fire
= Be careful/ Take care.Don't play with fire.
13.cross the road quickly when the trattic lights turn green
= Go across the road quickly when the trattic lights turn green.