Cho hàm số  y=21+x , dự đoán công thức y(n)(x) bằng:
A. (-1)n.n!(1+x)n+1
B. (-1)n.2.n!(1+x)n
C. 2.(-1)n.n!(1+x)n+1
D. 2.(-1)n+1.n!(1+x)n+1

Cho dãy số $\left( {{u}_{n}} \right)$ với$\displaystyle {{u}_{n}}=\frac{2n+b}{5n+3}$ trong đó$b$ là tham số thực. Để dãy số$\left( {{u}_{n}} \right)$ có giới hạn hữu hạn, giá trị của$b$ là
A. $b$ là một số thực tùy ý.
B. $b=2.$
C. không tồn tại $b.$ 
D. $b=5.$

A. 5.
B. 4.
C. 3.
D. 2.

A. N0 = 50.
B. N0 ≥ 51.
C. N0 = 40.
D. N0 = 45.

Find a mistake in the four underlined parts of the sentence and correct it:
Although she’s charming, but there’s something a little odd about her.
A. she’s
B. but
C. something
D. odd

A. 2.
B. 3.
C. 4.
D. 5.

Find a mistake in the four underlined parts of the sentence and correct it:
Most plants in deserts have adapted to sporadic rainfalls in a desert environments.
A. Most
B. have adapted
C. rainfalls
D. environments

Find a mistake in the four underlined parts of the sentence and correct it:
I would have saved some food for you if I knew you were going to be late.
A. would have saved
B. for you
C. knew
D. to be late

Find a mistake in the four underlined parts of the sentence and correct it:
Although species evolve differently, most of them adapt to a specific habitat or environment that best meets their survive needs.
A. Although
B. adapt
C. that
D. survive

Find a mistake in the four underlined parts of the sentence and correct it:
Our understanding and use of non-verbal cues in facial expressions and gestures are familiar to us nearly in birth.
A. Our understanding
B. in facial expressions
C. are familiar
D. in