1 Why don't we help poor children with giving them English lessons for free?

2 If he works hard, he can improve his English pronouncuation quickly

3 This cake has to be divided into three equal parts

4 Because Van forgot her umbrella, she got wet

5 The train which arrived two hour late broke down twice on the way 

6 Although Dick is an American, he got a French name

7 We're surprised that this boy replies intelligently

8 Because David was sich, he couldn't pass in his final exam

9 Last summer we stayed in a hotel which is very luxirious

10 In spite of studying very well, nobody likes her

11 Nobody else is as good as Lan

12 I suggest the machine should be checked before we use it

13 Although she studies very well, nobody likes her

1 B

2 C

3 D

4 A

5 A

6 B

7 D

8 D

9 D

10 C

11 B

12 C

V.

1 will be used

2 will live

3 to study 

4 had already gone

5 were - would think 

6 is introduced

7 had worked - found

8 were watching - started

9 take

10 arrived - had been evacuated

1. Hoa asked Thanh if he could lend her his iPad for a few minutes.

2. It is very important to talk to your family members every day.

3. If people didn't use too much fertilizer, lands wouldn't be being spoiled.

4. Temporary shelters should be provided for the earthquake victims.

5. More trees are going to be planted in the school yard.

6. He's the most intelligent member in my group.

7. Despite being tired, they tried to finish their project on time.

8. If I had enough money, I could buy this bike.

9. Covid-19 is known to do harm to our lungs.

3 D

4 A

5 B

6 A

7 C

8 C

9 C

10 D

11 B

12 D

13 A

14 D

15 A

16 C

V

1 A

2 B

3 C

4 C

5 A

3.D       4.A       5.B      6.A      7.C      8.B      9.C      10.D

11.B     12.D     13.A     14.D      15.A       16.C

V.   

1.D    2.B     3.C     4.D    5.B

A

Tổng cộng có 5 câu lận á mn😥

A   C  A  B  B

Lời giải:

a. Với $n$ nguyên khác -3, để $B$ nguyên thì:

$2n+9\vdots n+3$

$\Rightarrow 2(n+3)+3\vdots n+3$

$\Rightarrow 3\vdots n+3$

$\Rightarrow n+3\in\left\{\pm 1; \pm 3\right\}$

$\Rightarrow n\in\left\{-2; -4; 0; -6\right\}$

b. 

$B=\frac{2n+9}{n+3}=\frac{2(n+3)+3}{n+3}=2+\frac{3}{n+3}$

Để $B_{\max}$ thì $\frac{3}{n+3}$ max

Điều này đạt được khi $n+3$ là số nguyên dương nhỏ nhất

Tức là $n+3=1$

$\Leftrightarrow n=-2$

c. Để $B$ min thì $\frac{3}{n+3}$ min

Điều này đạt được khi $n+3$ là số nguyên âm lớn nhất 

Tức là $n+3=-1$

$\Leftrightarrow n=-4$