15.the room was very comfortable so we all fell asleep easily
16.It was very cold so they couldn't keep working in the field
17.He spoke slowly so we could understand him
18.The fair was very noisy so we couldn't hear each other
19. The soup is very excellent so we will have some. 
20. They stopped working because they were very tired
21. The question was very hard, therefore, we couldn't answer it  
22. The TV programmer is very exciting so the children won't miss it  
23. You're very young, so you can't drive that car 
24. She was tired so she didn't go anywhere 
25. These shoes are very small so I can't wear them  
26. He is so weak so he can't run.  
27. The coffee was very hot but I could drink it. 
28. He has a lot of money, so he can buy a car.  
29. He is very intelligent so he can do it. 
30. Tom is strong so he can lift the box. 
31. The weather is fine so Mary and her little brother can go to school.
32. The sun is not warm so We can't live on it. 
33. The water is quite warm so I can drink it.