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 53 to 62.

History books recorded that the first film with sound was The Jazz Singer in 1927. But sound films, or talkies, did not suddenly appear after years of silent screenings. From the earliest public performances in 1896, films were accompanied by music and sound effects. These were produced by a single pianist, a small band, or a full-scale orchestra; large movie theatres could buy sound-effect machines. Research into sound that was reproduced at exactly at the same time as the pictures – called “synchronized sound” – began soon after the very first films were shown. With synchronized sound, characters on the movie screen could sing and speak. As early as 1896, the newly invented gramophone, which played a large disc carrying music and dialogue, was used as a sound system. The biggest disadvantage was that the sound and pictures could become unsynchronized if, for example, the gramophone needle jumped or if the speed of the projector changed. This system was only effective for a single song or dialogue sequence.

In the “sound-on-film” system, sound was recorded as a series of marks on celluloid which could be read by an optical sensor. These signals would be placed on the film alongside the image, guaranteeing synchronization. Short feature films were produced in this way as early as 1922. This system eventually brought us “talking pictures”.

According to the passage, the word “sequence” is closest in meaning to_________.

A. interpretation

B. progression               

C. distribution              

D. organization

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.

        An air pollutant is defined as a compound added directly or indirectly by humans to the atmosphere in such quantities as to affect humans, animals, vegetation, or materials adversely. Air pollution requires a very flexible definition that permits continuous changes. When the first air pollution laws were established in England in the fourteenth century, air pollutants were limited to compounds that could be seen or smelled - a far cry from the extensive list of harmful substances known today. As technology has developed and knowledge of the health aspects of various chemicals has increased, the list of air pollutants has lengthened. In the future, even water vapor might be considered an air pollutant under certain conditions.

        Many of more important air pollutants, such as sulfur oxides, carbon monoxides and nitrogen oxides are found in nature. As the Earth developed, the concentration of these pollutants was altered by various chemical reactions; they became components in biogeochemical cycles. These serve as an air purification scheme by allowing the compounds to move from the air to the water or soil. On a global basis, nature's output of these compounds dwarfs that resulting from human activities.

        However, human production usually occurs in a localized area, such as a city. In such a region, human output may be dominant and may temporarily overload the natural purification scheme of the cycles. The result is an concentration of noxious chemicals in the air. The concentrations at which the adverse effects appear will be greater than the concentrations that the pollutants would have in the absence of human activities. The actual concentration need not be large for a substance to be a pollutant; in fact, the numerical value tells us little until we know how much of an increase this represents over the concentration that would occur naturally in the area. For example, sulfur dioxide has detectable health effects at 0. 08 parts per million (ppm), which is about 400 times its natural level. Carbon monoxide, however has a natural level of 0. 1 ppm and is not usually a pollutant until its level reaches about 15 ppm.

According to the passage, the numerical value of the concentration level of a substance is only useful if .

A. it can be calculated quickly

B. it is in a localized area 

C. the natural level is also known 

D. the other substances in the area are known

X là dẫn xuất đibrom sinh ra khi cho isopentan phản ứng với brom có chiếu sáng. Thủy phân hoàn toàn X cho hợp chất hữu cơ đa chức Y hòa tan được Cu(OH)₂. Số đồng phân cấu tạo thỏa mãn của Y là

A. 6

B. 4

C. 3

D. 8

Sự hiện diện của ADN là quan trọng cho các hoạt động trao đổi chất của tế bào vì ADN

A. chỉ đạo sản xuất các enzyme

B. là một thành phần cấu trúc của tế bào

C. trực tiếp làm tăng độ tan của các chất dinh dưỡng

D. là thành phần chính của tế bào chất