7 . No matter where you live in the world, natural disasters are always a threat. Of course, we humans take steps, both at an individual and social level, to prepare ourselves for the possibility of natural disasters. But preparing for these events requires understanding the types of natural disasters, what causes them, and the dangers they cause.
A technical term for a period of very cold weather, a cold wave is a type of natural disaster where the temperature drops rapidly over the course of 24 hours. While cold weather in itself isn’t necessarily enough to cause a natural disaster, a rapid dropping of the temperature could lead to lots of problems for communities in a region.
Interestingly, there isn’t an precise temperature threshold (起点) that must reach to be. Rather, cold waves are classified (分类) by how fast the temperature falls. Since what’s considered to be “cold” varies widely from region to region, local weather services will use local weather averages to determine if a weather event is actually a cold wave.
There are many reasons why a cold wave might occur. One of the most common causes of a cold wave is the arrival of a very strong high pressure system from the polar regions. Alternatively, movement in the jet streams can also drive very cold weather southward in just a matter of hours.
The primary danger of a cold wave is, indeed, the cold weather itself. This can lead to a higher risk of hypothermia (低温症) and other cold-related injuries. Additionally, cold weather can cause ice and frost to build up quickly, damaging basic facilities. Cold waves are also particularly dangerous for aircraft and other machinery. Extreme cold can use up vehicle batteries or cause petrol to come together. So, whenever in extreme cold weather, people need to be careful.
1. Why do people need to understand natural disasters?
| A．To remove nervousness. | B．To encourage research. |
| C．To get ready for its possibility. | D．To build professional departments. |
2. How can we define a cold wave?
| A．By an exact temperature. | B．By classified temperature. |
| C．By local climate standards. | D．By fallen temperature in summer. |
3. Which of the following contributes most to the cold wave?
| A．Sudden big wind. | B．Heavy snow. |
| C．Rapidly rising temperature. | D．A powerful pressure system from polar areas. |
4. What is the text mainly about?
| A．A natural program. | B．A climate disaster. |
| C．A scientific method. | D．A scientific experiment. |
