Có bao nhiêu giá trị nguyên của tham số m để phương trình 4 x − m .2 x + 1 + 2 m 2 − 5 = 0  có hai nghiệm nguyên phân biệ

A. 1  

B. 5   

C. 2   

D. 4

Lực ma sát nghỉ tác dụng lên vật có hướng?

A.Hướng vào tâm O

B.Hướng ra xa tâm O

C.Tiếp tuyến với quỹ đạo tròn

D.Còn phụ thuộc vào vận tốc góc  ω

Quá trình tự nhân đôi của ADN có các đặc điểm:

(1) Diễn ra ở trong nhân, tại kì trung gian của quá trình phân bào.

(2) Diễn ra theo nguyên tắc bổ sung và nguyên tắc bán bảo toàn.

(3) Cả hai mạch đơn đều làm khuôn để tổng hợp mạch mới.

(4) Mạch đơn mới được tổng hợp theo chiều 5'→ 3'.

(5) Khi một phân tử ADN tự nhân đôi 2 mạch mới được tổng hợp đều được kéo dài liên tục với sự phát triển của chạc chữ Y.

(6) Qua một lần nhân đôi tạo ra hai ADN con có cấu trúc giống ADN mẹ.

Có bao nhiêu đặc điểm đúng:

A. 5

B. 6

C. 3

D. 4

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 43 to 50.

          Carbon dating can be used to estimate the age of any organic natural material; it has been used successfully in archeology to determine the age of ancient artifacts or fossils as well as in a variety of other fields. The principle underlying the use of carbon dating is that carbon is a part of all living things on Earth. Since a radioactive substance such as carbon-14 has a known half-life, the amount of carbon-14 remaining in an object can be used to date that object.

          Carbon-14 has a half-life of 5,570 years, which means that after that number of years, half of the carbon- 14 atoms have decayed into nitrogen-14. It is the ratio of carbon-14 in that substance that indicates the age of the substance. If, for example, in a particular sample the amount of carbon-14 is roughly equivalent to the amount of nitrogen-14, this indicates that around half of the carbon-14 has decayed into nitrogen-14, and the sample is approximately 5,570 years old. 

          Carbon dating cannot be used effectively in dating objects that are older than 80,000 years. When objects are that old, much of the carbon-14 has already decayed into nitrogen-14, and the molecule amount that is left doesn’t provide a reliable measurement of age. In the case of older objects, other age-dating methods are available, methods which use radioactive atoms with longer half-lives than carbon has.

The word “underlying” could best be replaced by______.

A. below

B. requiring

C. serving as a basis for

D. being studied through

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.

             In the world today, particularly in the two most industrialized areas, North America and Europe, recycling is big news. People are talking about it, practicing it, and discovering new ways to be sensitive to the environment. Recycling means finding ways to use products a second time. The motto of the recycling movement is "Reduce, Reuse, Recycle".
            The first step is to reduce garbage. In stores, a shopper has to buy products in blister packs, boxes and expensive plastic wrappings. A hamburger from a fast food restaurant comes in lots of packaging: usually paper, a box, and a bag. All that packaging is wasted resources. People should try to buy things that are wrapped simply, and to reuse cups and utensils. Another way to reduce waste is to buy high-quality products. When low quality appliances break, many customers throw them away and buy new ones - a loss of more resources and more energy. For example, if a customer buys a high-quality appliance that can be easily repaired, the manufacturer receives an important message. In the same way, if a customer chooses a product with less packaging, that customer sends an important message to the manufacturers. To reduce garbage, the throwaway must stop.
            The second step is to reuse. It is better to buy juices and soft drinks in returnable bottles. After customers empty the bottles, they return them to the store. The manufacturers of the drinks collect the bottles, wash them, and then fill them again. The energy that is necessary to make new bottles is saved. In some parts of the world, returning bottles for money is a common practice. In those places, the garbage dumps have relatively little glass and plastic from throwaway bottles.
           The third step is being environmentally sensitive is to recycle. Spent motor oil can be cleaned and used again. Aluminum cans are expensive to make. It takes the same amount of energy to make one aluminum can as it does to run a color TV set for three hours. When people collect and recycle aluminum (for new cans), they help save one of the world's precious resources.

Which is described as one of the most industrialized areas?

A. Asia       

B. Middle East      

C. South America 

D. Europe