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long bi

Read the following text and mark the letter A, B, C or D on your answer sheet to indicate the correct answer to each of the questions

Many ants forage across the countryside in large numbers and undertake mass migrations; these activities proceed because one ant lays a trail on the ground for the others to follow. As a worker ant returns home after finding a source of food, it marks the route by intermittently touching its stinger to the ground and depositing a tiny amount of trail pheromone – a mixture of chemicals that delivers diverse messages as the context changes. These trails incorporate no directional information and may be followed by other ants in either direction.

Unlike some other messages, such as the one arising from a dead ant, a food trail has to be kept secret from members of other species. It is not surprising then that ant species use a wide variety of compounds as trail pheromones. Ants can be extremely sensitive to these signals. Investigators working with the trail pheromone of the leafcutter ant Atta texana calculated that one milligram of this substance would suffice to lead a column of ants three times around Earth.

The vapor of the evaporating pheromone over the trail guides an ant along the way, and the ant detects this signal with receptors in its antennae. A trail pheromone will evaporate to furnish the highest concentration of vapor right over the trail, in what is called a vapor space. In following the trail, the ant moves to the right and left, oscillating from side to side across the line of the trail itself, bringing first one and then the other antenna into the vapor space. As the ant moves to the right, its left antenna arrives in the vapor space.

The signal it receives causes it to swing to the left, and the ant then pursues this new course until its right antenna reaches the vapor space. It then swings back to the right, and so weaves back and forth down the trail.

What does the passage mainly discuss?

A. The information contained in pheromones

B. The mass migration of ants

C. How ants mark and follow a chemical trail

D. Different species of ants around the world

long bi

The weather is a national obsession in Britain, perhaps because it is so changeable. It's the national talking point, and most people watch at least one daily weather forecast. Most of the viewers imagine that the presenter does little more than arrive at the studio a few minutes before the broadcast, read the weather, and then go home. 

In fact, this image is far from the truth. The two-minute bulletin which we all rely on when we need to know tomorrow's weather is the result of a hard day's work by the presenter, who is actually a highly-qualified meteorologist.

Every morning, after a weather forecaster arrives at the TV studios, his/her first task of the day is to collect the latest data from the National Meteorological Office. The information is very detailed and includes predictions, satellite and radar pictures, as well as more technical data. After gathering all the relevant material from this office, the forecaster has to translate the scientific terminology and maps into images and words which viewers can easily understand. The final broadcast is then carefully planned. The presenter decides what to say and in what order to say it. Next a “story board” is drawn up which lays out the script word for word.

The time allocated for each broadcast can also alter. This is because the weather report is screened after the news, which can vary in length. The weather forecaster doesn't always know how much time is available, which means that he/she has to be thoroughly prepared so that the material can be adapted to the time available.

What makes weather forecasting more complicated is that it has to be a live broadcast and cannot be pre-recorded. Live shows are very nerve-racking for the presenter because almost anything can go wrong. Perhaps the most worrying aspect for every weather forecaster is getting the following day's predictions wrong. Unfortunately for them, this is not an unusual occurrence; the weather is not always possible to predict accurately.

These days, a weather forecaster's job is even more complicated because they are relied upon to predict other environmental conditions. For example, in the summer the weather forecast has to include the pollen count for hay fever sufferers. Some also include reports on ultraviolet radiation intensity to help people avoid sunburn. The job of a weather forecaster is certainly far more sophisticated than just pointing at a map and describing weather conditions. It's a job for professionals who can cope with stressful and challenging conditions.

Weather forecasters have to know the material well because _____.

A. the forecast may be incorporated into the news broadcast

B. they sometimes need to change it to meet the time limitation

C. the broadcast is pre-recorded

D. they don’t make the bulletins by themselves