A、Warning from NASA. B、How to treat Rift Valley Fever. C、The disastrous effects of Rift Valley Fever. D、Satellites and global he

IN DECEMBER 1997 large numbers of cattle, goats and sheep began dying in the Garissa district of north-eastern Kenya. A month later people started dying, too. It was, at the time, the biggest recorded outbreak of Rift Valley fever in east Africa. Some 100, 000 stock animals succumbed and about 90, 000 people were infected—hundreds fatally—in five countries.
   In December 2007 the same thing happened. Or, rather, it started to happen but was stopped in its tracks. The difference was that the second time around there was warning. In September researchers at the Goddard Space Flight Centre in Greenbelt, Maryland, part of America’s space agency, NASA, told the authorities in Kenya that they had a problem. They told them again in October. And again in November. By the time the epidemic emerged, the Kenyan health ministry had dispatched teams to the area to distribute mosquito nets and urge village leaders and religious authorities to stop people slaughtering and eating animals. Though the outbreak still killed 300 people in Kenya, Somalia and Tanzania, it could have been a lot worse. According to Kenneth Linthicum of America’s Department of Agriculture, the number of deaths would probably have been more than twice as high without the warning.
   The warning itself was possible because of a model of how disease spreads that Dr Linthicum helped design. And the data that were plugged into that model came from satellites.
   What the researchers at Goddard had noticed at the time of the first outbreak was that in the months preceding it, surface temperatures in the equatorial part of the Indian Ocean had risen by half a degree. These higher temperatures brought heavy and sustained rains, cloud cover and warmer air to much of the Horn of Africa. Mosquitoes multiplied wildly — and lived long enough for the virus that causes the fever to develop to the point where it is easily transmissible. In September 2007 the researchers saw the same thing happening in the ocean, and suspected the same consequences would follow.
Questions 26-30 are based on the passage you have just heard.
26. How many stock animals died as a result of the outbreak of the Rift Valley fever in 1997?
27. What helped stop the outbreak of the Rift Valley fever in 2007?
28. Which of the following is not mentioned as a measure to prevent the 2007 outbreak from spreading?
29. What triggered the two outbreaks of the Rift Valley fever in Africa?
30. What is the talk mainly about?