To many people, it is still just a dream to use a driverless car. But this dream is now becoming a    1    for people in the American state of Pennsylvania.

The ride-sharing service Uber will start using self-driving cars in a few weeks to carry passengers around the city of Pittsburgh.

Many companies, including Google, Apple and the big U.S. carmakers, are    2    testing driverless vehicles. But this is the first time the American public will    3    get to use them.

The ride service will start out with Ford Fusions    4    with self-driving technology. People using Uber will request the cars through their smartphones. Rides in the self-driving vehicles will be free while the system is    5    in Pittsburgh. Each car will have a driver in front, as a safety measure, to take control of the vehicle if    6    .

Uber also announced a $300 million    7    with an automobile manufacturer, Volvo, to cooperate on self-driving technology and supply vehicles. In the future, Volvo vehicles will be part of the driverless fleet in Pittsburgh.

Kalra, an information scientist with the not-for-profit RAND Corporation, believes driverless cars will be used by car-sharing services in other cities in the coming years. But she said companies like Uber and its main competitor, Lyft, will have to consider several issues before    8    These include laws    9    self-driving technology, population, climate and terrain - the shape and condition of the land.

As for the users, Kalra said they are likely to accept autonomous driving technology very fast. “If the technology is    10    safe, and it behaves in a way that they expect drivers to behave, then I think people will get comfortable very quickly - because it offers so many other benefits.”

Scientists have found strong evidence that soot, or black carbon, sent into the air by a rapidly industrializing Europe, likely caused the sudden retreat (moving back) of mountain glaciers (冰川) in the European Alps. The research may help solve a longstanding scientific    1    about why the Alps glaciers retreated beginning in the 1860s, decades before global temperatures started rising again.

Glacier records in the central European Alps    2    back to the 1500s show that between 1860 and 1930,    3    defined as the end of the Little Ice Age in Europe, large valley glaciers in the Alps suddenly retreated by an average of nearly 0.6 mile. Yet weather in Europe cooled by nearly 1.8 degrees Fahrenheit during that time. Glaciologists and climatologists have struggled to understand the    4    between the climate and glacier records.

To investigate, Thomas Painter, a snow and ice scientist, and his colleagues turned to    5    . In the decades following the 1850s, Europe was    6    a powerful economic and atmospheric transformation stimulated by. industrialization. Residents, transportation, and perhaps most    7    , industry in Western Europe began burning coal in huge quantities of black carbon into the atmosphere.

When black carbon particles (粒子) settle on snow, they darken the surface. This melts the snow and    8    the underlying glacier ice to sunlight and relatively warm air earlier in the year, allowing more and faster melt.

“This study    9    some likely human fingerprints on our changing environment,” Painter said. “It’s a    10    that the actions we take have far-reaching impacts on the environment in which we live. We must now look closer at other regions on Earth, such as the Himalaya, to study the present-day impacts of black carbon on glaciers.”