giúp em với ạ và giải thích nữa ạ (em đang cần) 
16. David (be) born after his father (die) 

17. What you (do) at one o’clock this morning?                                                          
  18. Up to now, the teacher (give) our class five tests.

19. My uncle (not give) up (smoke) after the doctor (tell) him he risked (have) a heart attack if he continued 

20. There is an international football match on TV tonight. Liverpool (play) against Manchester   
   21.He dreads (have) to retire 

22. You (manage) (finish) (pack) these parcels last night?                                      
   23. Don’t forget (lock) the door before (go) to bed

24. Are you free this afternoon? No, I am not. I (attend) a lecture given by Professor Jones

25. Mary (drive) to work every day, but today she (wait) for the bus .                       
26. I can’t wait until the weekend (come)

27.These boys (work) in the garden for three hours                                                
    28. The roads (widen)  so we have to find another way