More recent research has shown that many kinds of amphibians(两栖动物) are declining or have become extinct. Amphibians are animals, such as frogs, that live partly in water and partly on land. And they have been around for over 350 million years. They have     1     three mass extinctions, including the     2     of the dinosaurs. Why are they dying out now?

The most serious aspect of amphibian loss, however, goes beyond the amphibians themselves. Scientists are beginning to think about what amphibian     3     means for the planet as a whole. If the earth is becoming unlivable for amphibians, is it also becoming unlivable for other kinds of animals and human beings as well?

Scientists now believe that amphibian decline is due to several environmental factors. One of these factors is the     4     of habitat, the natural area where an animal lives. Amphibians are very     5     to changes in their habitat. If they cannot find the right conditions, they will not lay their eggs. These days, as wild areas are covered with houses, roads, farms, or factories, many kinds of amphibians are no longer laying eggs.

There are a number of other factors in amphibian decline. Pollution is one of them. In many industrial areas, air pollution has     6     the rain, which then falls on ponds and kills the frogs that live there. In farming areas, the heavy use of     7     on crops has also killed off amphibians. Another factor is that air pollution has led to    8     levels of ultraviolet (UV) light. This endangers amphibians, which seem to be     9     sensitive to UV light.

All these reasons for the disappearance of amphibians are also good reasons for more general     10     . These factors affect human beings, too.

Destinations around the world have faced significant tourist reductions amid the coronavirus pandemic. But few have taken a harder    1    than Bali, the Indonesian island long beloved of global travelers. Due to strict     2    control measures and a closed airport, Bali went from receiving millions of international visitors to welcoming just 45 in 2021. The two-digit number accounts for the period between January and October 2021 and was    3    by the Central Statistics Bureau of Bali.

As the island's Ngurah Rai International Airport（DPS）in Denpasar has been closed to international flights nearly all year, those tourists have almost all come via private yachts. Though the airport officially reopened to international flights on October 14, there have so far only been domestic flights in and out of the airport,    4    from Indonesia's capital city of Jakarta.

In order to come to Bali, foreign tourists have to deal with strict Covid-related entry requirements. They must obtain a business visa at a cost of $300（there are no tourist visas at present）, take multiple PCR tests and buy special health     5    . In addition, airfare costs are higher than usual due to the lack of direct flights.

One hopeful visitor is Justyna Wrucha, a UK citizen planning a trip to Bali with her husband. It will be their first visit to the island, which has long been on their bucket list. However, they think that the policies relating to foreign visitors are extremely harsh by    6    a 10-day quarantine on fully    7    people.

Bali's Covid policies are determined by the central government in Jakarta, not by local authorities on the island. Originally, the quarantines were shorter but were recently increased due to fears of the new Omicron    8    . Ray Suryawijaya, head of the Indonesian Hotels and Restaurants Association of Bali's Badung District, agrees with Wrucha. "With all those barriers, it's difficult for us to expect foreign tourists to come to Bali," he said.

However, there is one small glimmer of hope with the gradual return of domestic tourism. Ray reports that the    9    rate of hotels in Bali is now around 35%. "On weekends, about 13,000 domestic tourists are visiting Bali," he adds. While that small trickle of visitors is an    10    note to end the year on, especially for the many Balinese locals who depend on tourism to support their families, it won't be enough to rescue the 2021 season.

Sense of smell is our most rapid warning system

“The human avoidance response to unpleasant smells associated with danger has long been seen as a    1     perceivable process, but our study shows for the first time that it’s unconscious and extremely rapid,” says the study’s first author Behzad Iravani, researcher at the Department of Clinical Neuroscience, Karolinska Institutet.

The organ relating to the sense of smell takes up about five per cent of the human brain and enables us to    2    between many million different smells. A large proportion of these smells are associated with a threat to our health and    3    , such as that of chemicals and rotten food. Smell signals reach the brain within 100 to 150 milliseconds after being breathed in through the nose.

The survival of all living organisms depends on their ability to avoid danger and seek    4    . In humans, the smell sense seems particularly important for detecting and reacting to    5    harmful substance.

It has long been a mystery just which sensory systems are involved in the change of an unpleasant smell into avoidance behavior in humans. Researchers at Karolinska Institutet have now    6    a method that for the first time has made it possible to measure signals from the human smell organ, which processes smells and in turn can    7    signals to parts of the brain that control movement and avoidance behavior.

Their    8     are based on three experiments in which participants were asked to rate their   experience of six different smells, some positive, some negative, while the electrophysiological activity of the smell organ when    9    to each of the smells was measured.

“It was clear that the organ reacts specifically and    10    to negative smells and sends a direct signal to the outer layer of the organ within about 300 ms,” says the study’s last author Johan Lundström. ” The signal causes the person to unconsciously lean back and away from the source of the smell.”