14. from -> since (HTHTTD nên dùng since)
15. with -> by (learn by heart: học thuộc lòng)
16. have been -> has been (Mathematics tuy có s ở cuối nhưng là số ít)
17. to wait -> waiting (mind Ving)
18. don't lock -> not to lock (told S to V/ not to V)
14. from -> since
15. with -> by
16. have been -> has been
17. to wait -> waiting
18. don't lock -> not to lock