12  I suggest he should turn off the lights when going to the bed.

13 If you work hard, you will pass the exam.

14 Because the snow is heavy, we had to stop working.

15 Unless you start working hard now, you won't be able to pass the final exam.

16 Since I'll be on vacation next week, I won't be able to attend the meeting.

17 Because of the crack in the water pipes, the water bill was enormous.

18 He speaks English fluently.

19 They stopped going out with him almost two years ago. 

20 If he works hard, Nam will be successful.