IV. Choose the correct option for each gap to finish the passage A tsunami is a chain of fast moving waves in the ocean caused by powerful earthquakes or volcanic eruptions. Tsunami has a very long wave. It can be hundreds of kilometers (16) _______ Usually, tsunami starts suddenly. The waves travel (17) _________ a great speed across an ocean with little energy loss. They can remove sand from beaches, destroy trees, toss and drag vehicles, damage houses and even destroy whole towns. The water will draw back from the coast half of the wave period prior to the wave getting to the coast. If the slope of the coast is not deep, the water may (18) __________ for hundreds of metres. People who do not know of the danger will often remain at the shore. Tsunamis cannot (19) _________ . However, there are ways to help stop people from dying from a tsunami. Some (20) __________ with lots of tsunamis may use warning systems which may warn the population before the big waves reach the land. Because an earthquake that caused the tsunami can be felt before the wave gets to the shore, people can be warned to go somewhere safe. 16. A. long B. far C. wide D. large 17. A. from B. of C. at D. in 18. A. rise        B. raise        C. arise        D. raising 19. A. prevent B. go along C. spread out D. be prevented 20. A. countries B. regions C. states D. districts