题目内容
Two scientists from the United States have been traveling to countries in South America to study lightning storms. Rather than observing the lightning from the ground, scientists are watching the lightning from airplanes that fly at high altitudes(海拔) above the surface of Earth. The splendid phenomena—which have been given the imaginary names of “red sprites,” “blue jets,” and “elves”—occur high in the atmosphere above the clouds.
During some storms a sudden flash of light will spread over the upper atmosphere with a red light that can extend as far as 60 miles above Earth. Known as a sprite, this lightning appears in the sky often in the shape of a huge carrot or jellyfish in groups of two or more. Blue jets are flashes of blue light that emanate from the top of thunderstorms and then spreading upward as much as 20 miles above Earth. These jets of light can increase in size at speeds near 60 miles per second. Elves are the most recently discovered type of high-altitude lightning. These flashes take place 40 to 60 miles above Earth and often appear just before sprites and are much brighter than sprites. Because they occur too fast to be seen with eyes, they can be detected only by instruments.
Although scientists do not have a certain explanation for the phenomena, they are making some progress. For example, one popular theory is that the light seen from the red sprites and blue jets results from the collision(碰撞) of electrically charged tiny bits with nitrogen molecules(氮分子) in Earth’s atmosphere. The collision causes molecules to shine blue in the stratosphere, or lower altitudes. These same molecules shine red in the mesosphere, the atmosphere above the stratosphere, and they can spread to an altitude of about 50 miles. Elves seem to be caused when forceful lightning hits the ground and sends electrically charged bits into the higher altitudes.
1．What is the common characteristic of “red sprites,” “blue jets” and “elves”?
A．They are sudden blue flashes.
B．They can only be discovered by equipment.
C．They are caused by the collision of atmosphere.
D．They spread upward 20 to 60 miles above Earth.
2．The words “emanate from” underlined in paragraph 2 probably mean .
A．come from B．result from C．break away from D．range from
3．What is the third paragraph about?
A．A research about the Earth. B．The causes of the collision.
C．An explanation for the phenomena. D．Different theories about lightning.
4．What is the best title of this passage?
A．A Frightening Study. B．Movement of the Molecules.
C．The Changeable Atmosphere. D．Lightning above the Clouds.
DACD
