cho lăng trụ đứng abc.a'b'c' có đáy abc là tam giác vuông cân tại a, ab=ac=a, aa1=a√2. Gọi M,N lần lượt là trung điểm aa1,bc1. chứng minh MN là đường vuông góc chung của aa1 và bc1. tính thể tích khối chóp ma1bc1

cho hình chóp sabc, abc là tam giác vuông, ab=a, góc bac=60°. sa vuông abc, sb tạo mp(sac) 30°. tính thể tích hình chóp

Bảng dưới đây ghi lại hiện tượng khi làm thí nghiệm với các chất X, Y, Z, T ở dạng dung dịch với dung môi nước:

Các chất X, Y, Z, T lần lượt là:

A. Phenol, axit fomic, saccarozơ, glucozơ

B. Anilin, glucozơ, glixerol, frutozơ

C. Anilin, glucozơ, etanol, axit acrylic

D. Phenol, glucozơ, glixerol, mantozơ

VIII/ 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 following questions from 56 to 65.

Psychologists have debated a long time about whether a child’s upbringing can give it the ability to do outstandingly well. Some think that it is impossible to develop genius and say that it is simply something a person is born with. Others, however, argue that the potential for great achievement can be develop. The truth lies somewhere between these two extremes.

It seems very obvious that being born with the right qualities from gifted parents will increase a child’s ability to do well. However, this ability will be fully realized only with the right upbringing and opportunities. As one psychologist says, “To have a fast car, you need both a good engine and fuel.”

Scientists have recently assessed intelligence, achievement, and ability in 50 sets of identical twins that were separated shortly birth and brought up by different parents. They found that achievement was based on intelligence, and later influenced by the child’s environment.

One case involving very intelligent twins was quoted. One of the twins received a normal upbringing, and performed well. The other twin, however, was brought up by extremely supportive parents and given every possible opportunity to develop its abilities. That twin, though starting out with the same degree of intelligence as the other, performed even better.

This case reflects the general principle of intelligence and ability. The more favorable the environment, the more a child’s intelligence and ability are developed. However, there is no link between intelligence and socioeconomic level of a child’s family. In other words, it does not matter how poor or how rich a family is, as this does not affect the intelligence.

Gifted people can not be created by supportive parents, but they can be developed by them. One professor of music said that outstanding musicians usually started two or three years earlier than ordinary performers, often because their parents had recognized their ability. These musicians then needed at least ten years’ hard work and training in order to reach the level they were capable of attaining.

People who want to have very gifted children are given the following advice:

-     Marry an intelligent person.

-     Allow children to follow their own interests rather than the interests of the parents.

-     Start a child’s education early but avoid pushing the child too hard.

-      Encourage children to play; for example, playing with musical instrument is essential for a child who wants to become an outstanding musician.

Scientists chose twins for their study because x . 

A. they have the same genetic background, usually with similar intelligence 

B. they are born into the same family, hence the same upbringing 

C. they have the same economic background and hence the same opportunities 

D. each twin has the same environment as his/ her twin

Cho X, Y, Z, T  là các chất khác  nhau trong số 4 chất: CH₃COOH, C₆H₅COOH (axit benzoic), C₂H₅COOH, HCOOH và giá trị nhiệt độ sôi được ghi trong bảng sau:

Nhận xét nào sau đây là đúng ?

A. Y là CH₃COOH

B.  Z là HCOOH

C. X là C₂H₅COOH

D. T là C₆H₅COOH

VII/ 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 following questions from 46 to 55.

The White House, the official home of the United States president, was not built in time for George Washington to live in it. It was begun in 1792 and was ready for its first inhabitants. President and Mrs. John Adams, who moved in on November 1, 1800. When the Adams moved in, the White House was not yet complete, and the Adams suffered many inconveniences; for example, the main staircase was incomplete, which hindered movement from floor to floor, and the future laundry yard was merely a pool of mud, so wet laundry was hung in the unfinished East Room to dry. Thomas Jefferson, the third president, improved the comfort of the White House in many respects and added new architectural features such as the terraces on the east and west ends.

When the British forces burned the White House on August 24, 1814, President Madison was forced to leave. All the remained after the fire was the exterior walls, the interior was completely destroyed. It was not until December of that the following president, James Monroe, was able to move into a rebuilt residence. Since then, the White House has continued to be modified but has been continuously occupied by each succeeding U.S president.

The paragraph following the passage most likely discusses x  

A. the details of the destruction of the White House by the British. 

B. James Monroe’s policies as presidents. 

C. modifications by presidents who followed. 

D. other presidents who were unable to occupy the White House.

Cho 1,82 gam hợp chất hữu cơ, mạch hở X có công thức phân tử C₃H₉O₂N tác dụng vừa đủ với dung dịch NaOH đun nóng, thu được khí Y và dung dịch Z. Cô cạn Z thu được 1,64 gam muối khan. Tên gọi của X là :

A. Etylamoni fomat

B. Đimetylamoni fomat

C. Amoni propionat

D. Metylamoni axetat

Khi thủy phân peptit có công thức hóa học:

H₂N-CH(CH₃)-CONH-CH₂-CONH-CH₂-CONH-CH₂-CONH-CH(CH₃)-COOH  thì sản phẩm thu được có tối đa bao nhiêu peptit có phản ứng màu biure?

A. 4   

B. 5   

C. 10 

D. 3