I. Choose the best answer to complete the following sentences
1. These T-shirts and jeans __________ in the US. in 1900.
A. have made B. made C. were made D. make
2. The building is very dangerous. It __________ down next week.
A. knocked B. will knock C. will be knocked D. was knocked
3. The room looks nice. It __________
A. was cleaning B. has just been cleaned C. will be cleaned D. is cleaning
4. We ………… each other for 10 years.
A. know B. knew C. have known D. had known
5. Our twenty houses __________ when the fire engine __________
A. had burnt up / arrived B. burnt up / had arrived
C. had been burnt up / arrived D. will have burnt / arrives
6. After I __________ the grass, it __________ to rain.
A. have watered / will begin B. water / began
C. had watered / began D. had watered / will have begun
7. Next week when there __________ a full moon, the ocean tides will be higher.
A. is being B. is C. will be D. will have been
8. English is __________ all over the world.
A. spoken B. speak C. speaks D. to speak
9. Where will these coconut trees __________?
A. be planted B. planted C. plant D. be planting
10. Before Jane won the lottery, she __________ any kind of contest.
A. hasn’t entered B. doesn’t enter C. wasn’t entering D. hadn’t entered
11. My parents __________ tomorrow to stay with me for a few days.
A. come B. will have come C. are coming D. came
12. She left home in 1993 and __________ since then.
A. hasn’t seen B. didn’t see C. hasn’t been seen D. wasn’t seen
13.__________ your house painted last year?
A. Had B. Did C. Was D. Have
14. What __________ you __________ at 8 o’clock last night?
A. did/ do B. have/ done C. were/ doing D. had/ done
III. Mark the letter A, B, C, or D to show the underlined part that needs correction.
1. The children were frightening by the thunder and lightning.
A B C D
2. Two people got hurt in the accident and were took to the hospital by an ambulance.
A B C D
3. The students helped by the clear explanation that the teacher gave.
A B C D
4. That alloy is composing by iron and tin.
A B C D
5. The winner of the race hasn’t been announcing yet.
A B C D
6. Progress is been made every day in all parts of the world.
A B C D
7. When, where and by whom has the automobile invented?
A B C D
8. Each assembly kit is accompany by detailed instruction.
A B C D
\(A=\frac{n-2}{n+3}\)
a) Để A là phân số khi n+3 khác 0 ( n thuộc Z)
vậy n khác -3 ( n thuộc Z ) thì A là phân số
b) Để A nguyên khi n-2 chia hết cho n+3
mà n+3 chia hết cho n+3
suy ra n+3-(n-2) chia hết cho n+3
suy ra 5 chia hết cho n+3
n +3 \(\in\left\{1;-1;5;-5\right\}\)
n \(\in\left\{-2;-4;2;-8\right\}\)
Thử lại
\(B=\frac{10n-3}{4n-10}=\frac{\left(4n-10\right).\frac{5}{2}+22}{4n-10}\)
\(B=\frac{5}{2}+\frac{22}{4n-10}\Rightarrow B=\frac{5}{2}+\frac{11}{2n-5}\)
ĐỂ B đạt GTLN khi \(\frac{11}{2n-5}\)đạt GTLN, điều này xảy ra khi 2n - 5 là số nguyên dương nhỏ nhất,
tức là 2n-5=1 suy ra 2n=6 suy ra n=3
Khi đó \(B=\frac{10.3-3}{4.3-10}=\frac{27}{2}\)
Vậy B có GTLN là 27/2 khi n