Tìm một số biết

a) 1 6 7 của nó bằng 26

b) 60% của nó bằng  - 1 3 .

Tìm tổng các phân số lớn hơn - 1 7 , nhỏ hơn - 1 8  và có tử là -3

Read the following passage and mark the letter A, B, tr or I) to indicate the correct answer to each of the questions from 36 to 42.

Humans have struggled against weeds since the beginnings of agriculture. Marring our gardens is one of the milder effects of weeds - any plants that thrive where they are unwanted. They clog waterways, destroy wildlife habitats, and impede fanning. Their spread eliminates grazing areas and accounts for one-third of all crop loss. They compete for sunlight, nutrients, and water with useful plants.

The global need for weed control had been answered mainly by the chemical industry. Its herbicides are effective and sometimes necessary, but some pose serious problems, particularly if misused. Toxic compounds threaten animal and public health when they accumulate in food plants, groundwater, and drinking water. They also harm workers who apply them.

In recent years, the chemical industry has introduced several herbicides that are more ecologically sound. Yet new chemicals alone cannot solve the world's weed problems. Hence, scientists are exploring the innate weed-killing powers of living organisms, primarily insects and microorganisms.

The biological agents now in use are environmentally benign and are harmless to humans. They can be chosen for their ability to attack selected targets and leave crops and other plants untouched. In contrast, some of the most effective chemicals kill virtually all the plants they come in contact with, sparing only those that are naturally resistant or have been genetically modified for resistance. Furthermore, a number of biological agents can be administered only once, after which no added applications are needed. Chemicals typically must be used several times per growing season.

With what topic does this passage primarily deal?

A. The importance of the chemical industry.

B. The dangers of toxic chemicals.

C. A proposal to ban the use of all herbicides.

D. Advantages of biological agents over chemical ones.

Read the following pasage and mark the letter A,B,C or D to indicate the correct answer to each of the questions from 36 to 42.

A rather surprising geographical feature of Antarctica is that a huge freshwater, one of the world's largest and deepest, lies hidden there under four kilometers of ice. Now known as Lake Vostok, this huge body of water is located under the ice block that comprises Antarctica. The lake is able to exist in its unfrozen state beneath this block of ice because its waters are warned by geothermal heat from the earth's core. This thick glacier above Lake Vostok actually insulates it from frigid temperatures (the lowest ever recorded on Earth) on the surface.

The lake was first discovered in the 1970s while a research team was conducting an aerial survey of the area. Radio waves from the survey equipment penetrated the ice and revealed a body of water of indeterminate size. It was not until much more recently that data collected by satellite made scientists aware of the tremendous size of the lake; satellite-borne radar detected an extremely flat region where the ice remains level because it is floating on the water of the lake.

The discovery of such a huge fresh water lake trapped under Antarctica is of interest to the scientific community because of the potential that the lake contains ancient microbes that have survived for thousands upon thousands of years, unaffected by factors such as nuclear fallout and elevated ultraviolet light that have affected organisms in more exposed areas. The downside of the discovery, however, lies in the difficulty of conducting research on the lake in such a harsh climate and in the problems associated with obtaining uncontaminated samples from the lake without actually exposing the lake to contamination. Scientists are looking for possible ways to accomplish this.

The purpose of the passage is to ________

A. explain how Lake Vostok was discovered

B. provide satellite data concerning Antarctica

C. discuss future plans for Lake Vostok

D. present an unexpected aspect of Antarctica's geography

Tính giá trị của biểu thức: C = (x - 7).(x + 3) với x = -3