Cho dãy số u n được xác định như sau: u 1 = 2 u n + 1 + 4 u n = 4 − 5 n n ≥ 1 .  Tính tổng S = u 2018 − 2 u 2017 .

A.  S = 2015 − 3.4 2017

B.  S = 2016 − 3.4 2018

C.  S = 2016 + 3.4 2018

D.  S = 2015 + 3.4 2017

REVIEW

21. Because he sits around too much, he isn't fit

-> if he

22. Rita was exhausted because she didn't get any sleep

-> if rita

23. She's very thin; perhaps that's why she feels cold so much

-> if she

24. He never polishes his shoes, so he never looks smart

-> if he

25. He can't park near his office;that's whyvhe doesn' come by car

-> if he

26. My house is guarded by two big dogs. That's the only reason it isn't broken into every night

-> if my house

27. The flats were not clearly numbered, so it was very difficult to find them

-> if the flats