Polime dùng để sản xuất tơ lapsan có cấu tạo như sau:

Tên gọi của polime trên là

A. poliacrilonitrin.

B. poli(hexametylen ađipamit).

C. poli(etylen terephtalat).

D. policaproamit.

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 34 to 40.

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 change. 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 the more important air pollutants, such as sulfur oxides, carbon monoxide, 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 increased 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, human-generated air pollution in localized regions _____.

A. can be dwarfed by nature's output of pollutants

B. can overwhelm the natural system that removes pollutants

C. will damage areas outside of the localized regions

D. will react harmfully with natural pollutants

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.

       Geographers say that what defines a place are four properties: soil, climate, altitude, and aspect, or attitude to the Sun. Florida’s ancient scrub demonstrates this principle. Its soil is pure silica, so barren it supports only lichens as ground cover. (It does, however, sustain a sand- swimming lizard that cannot live where there is moisture or plant matter the soil.) Its climate, despite more than 50 inches of annual rainfall, is blistering desert plant life it can sustain is only the xerophytic, the quintessentially dry. Its altitude is a mere couple of hundred feet, but it is high ground on a peninsula elsewhere close to sea level, and its drainage is so critical that a difference of inches in elevation can bring major changes in its plant communities. Its aspect is flat, direct, brutal – and subtropical. Florida’s surrounding lushness cannot impinge on its desert scrubbiness.

       This does not sound like an attractive place. It does not look much like one either; Shrubby little oaks, clumps of scraggly bushes, prickly pear, thorns, and tangles. “It appear Said one early naturalist,” to desire to display the result of the misery through which it has Passed and is passing.” By our narrow standards, scrub is not beautiful; neither does it meet our selfish utilitarian needs. Even the name is an epithet, a synonym for the stunted, the scruffy, the insignificant, what is beautiful about such a place?

       The most important remaining patches of scrub lie along the Lake Wales Ridge, a chain of paleoislands running for a hundred miles down the center of Florida, in most places less than ten miles wide. It is relict seashore, tossed up millions of years ago when ocean levels were higher and the rest of the peninsula was submerged. That ancient emergence is precisely what makes Lake Wales Ridge so precious: it has remained unsubmerged, its ecosystems essentially undisturbed, since the Miocene era. As a result, it has gathered to itself one of the largest collections of rare organisms in the world. Only about 75 plant species survive there, but at least 30 of these are found nowhere else on Earth.

The author suggests that human standards of beauty are _______.

A. idealistic

B. limited

C. tolerant

D. defensible

Mark the letter A, B, C, or D on your answer sheet to indicate the word(s) OPPOSITE in meaning to the underlined word(s) in each of the following questions.

These boys are mischievous.

A. well-behaved

B. naughty 

C. fractious 

D. disobedient