mọi người làm sai hết rùi cô mình dạy thế này

2¹⁹³⁰.9¹⁹⁴⁵ = 4.2¹⁹²⁸.9¹⁹⁴⁴.9 = 36.(...6).(...1) = (...6)

=> có tận cùng là chữ số 6

Kết luận nào sau đây là đúng? 

A. Ancol etylic và phenol đều tác dụng được với Na và với dung dịch NaOH

B. Phenol tác dụng được với dung dịch NaOH và với dung dịch brom

C. Ancol etylic tác dụng được với Na nhưng không tác dụng được với CuO đun nóng.

D. Phenol tác dụng được với Na và tác dụng được với axit HBr

câu 1

gọi p, e, n, e', p', n' lần lượt là số p số e số n trong A và B

Ta có:

p+e+n+p'+n'+e'=78

(p+e+p'+e')-(n+n')=26

(p+e)-(p'+e')=28

=>2p+2p'+n+n'=78(1)

2p+2p'-(n+n')=26(2)

2p-2p'=28

Cộng (1) (2) ta có :

4p+4p'=104

2p-2p'=28

=>p=20

p'=26

vậy A là canxi B là cacbon

Số đối của số phức x = -1 + 2i là

A. w = -2+i

B. w = -1 - 2i

C. w = 1-2i

D. w = 1+2i

Mark the letter A, B, C, or D on your answer sheet to indicate the underlined part that needs correction in each of the following questions.

The Prime Minister is to consider changes to sexually discrimination laws to enforce equal opportunities.

A. is

B. to

C. discrimination

D. enforce

Read the following passage and mark the letter A, B, C, or D on your answer sheet to indicate the correct answer to each of the questions from 30 to 34.

Genetic modification of foods is not a new practice. It has been practiced for thousands of years under the name of "selective breeding". Animals and plants were chosen because they had traits that humans found useful. Some animals were larger and stronger than others, or they yielded more food, or they had some other trait that humans valued. Therefore, they were bred because of those traits. Individuals with those traits were brought together and allowed to breed in the hope that their offspring would have the same traits in greater measure.

Much the same thing was done with plants. To produce bigger or sweeter fruit, or grow more grain per unit of land, strains of plants were combined and recombined to produce hybrids, or crossbreeds that had the desired traits in the right combinations. All the while, however, biologists wondered: is there a more direct and versatile way to change the traits of plants and animals? Could we rewrite, so to speak, the heredity of organisms to make them serve our needs better?

In the 20th century, genetic modification made such changes possible at last. Now, it was possible to alter the genetic code without using the slow and uncertain process of selective breeding. It even became possible to blend plants and animals genetically: to insert animal genes into plants, for example, in order to give the plants a certain trait they ordinarily would lack, such as resistance to freezing. The result was a tremendous potential to change the very nature of biology.

What is the passage mainly about?

A. The arguments against genetic modification

B. The benefits brought about by genetic modification

C. The reasons behind selective breeding of plants

D. The development of genetic modification