题目内容：
Listening device provides landslide early warning A device that provides early warning of landslide by monitoring vibrations in soil is being tested by UK researchers．The device could save thousands of lives each year by warning when an area should be evacuated，the scientists say．Such natural disasters are common in countries that experience sudden，heavy rainfall，and Can also be triggered by earthquakes and even water erosion． Landslides start when a few particles of soil or rock Within a slope start to move，but the early stages can be hard to spot．Following this initial movement．“Slopes can become unstable in a matter of hours of minutes，”says Nell Dixon at Loughborough University，UK．He says a warning system that monitors this movement might be enough to evacu。 ate a block of flats or clear a road，and save lives．
The most common way to monitor a slope for signs of an imminent landslide is to watch for changes in its shape．Surveyors can do this by monitoring a site directly，or sensors sunk into boreholes or fixed above ground can be sued to monitor the shape of a slope．Slopes can，however，change shape without triggering a landslide，so either method is prone to causing false alarms．Now Nixon’s team has developed a device that listens for the vibrations caused when partieles begin moving within a slope．
The device takes the form of steel pipe dropped into a slope．The borehole is filled in with gravel around the pipe to help transmit high—frequency vibrations generated by particles within the slope．These vibrations pasg up the tube and are picked up by a sensor on the surface．Software analyses the vibration signal to determine whether a landslide may be imminent．
The device is cmTently being tested in a 6一metre—tall artificial clay embankment in Newcastle．UK．Early results suggest it should provide tewer false positives than existing systems．Once it has been carefully and thoroughly tested，the device could be used to create a complete early—warning system for dangerous slopes．
“Locations with a significant risk of landslides could definitely benefit from a machine like this，”says Adam Poulter，an expert at the British Red Cross．“As long as it doesn’t cost too much．”But，Pouher adds that an early—warning system may not be enough on it own．“You need to have the human communication，”he says．“Making systems thatget warnings to those who need them can be difficult．”根据以上材料回答下面问题：What does“Such natural disasters”in the first paragraph refer to? A．Sudden,heavy rainfal
B．Earthquakes
C．Water erosion
D．Landslides
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