单选题
- A. They are tidal waves.
- B. They can be caused by the fall of an asteroid into the water.
- C. They can not be detected before they hit land.
- D. They are harbor waves.
单选题
- A. Tsunamis are caused by underwater earthquakes.
- B. Earthquakes of about magnitude 6.75 on the Richter scale will cause
tsunamis.
- C. Nearly 90 percent of underwater earthquakes cause tsunamis.
- D. Not all underwater earthquakes cause tsunamis.
单选题
- A. The first wave is often the largest.
- B. The wave following large volume of water is usually not very long but
very tall.
- C. The wave of tsunamis can spread across the sea in all directions.
- D. The wave of tsunamis usually travels at a lower speed at the
beginning.