有60克溶质质量分数为10%的硝酸钠溶液，欲将其溶质质量分数增加一倍，应该采取的
题型：多选题
问题：
| 有60克溶质质量分数为10%的硝酸钠溶液，欲将其溶质质量分数增加一倍，应该采取的方法是（ ） A．把溶剂蒸发掉 B．加入7.5克硝酸钠固体 C．把溶剂蒸发掉30克 D．加入20%的硝酸钠溶液30克 |
题型：多选题
简答题（共3小题；每小题1.5分，满分4.5分）
Tsunamis (海啸) are a series of huge waves created by an underground movement such as an earthquake or a volcanic eruption (火山喷发) . A tsunami can travel hundreds of miles per hour in the open ocean and hit the land with huge waves.
From the area where the tsunamis come, waves travel in all directions. Once the waves approach the coast, the
y will become more than 100 feet in height. The topography (地形) of the coastline and the ocean floor will influence the size of the wave. There may be more than one wave and the latter one may be larger than the one before. That is why a small tsunami at one beach can be a huge wave a few miles away.
All tsunamis are dangerous, even if they may not damage every coastline they strike. A tsunami can strike anywhere along most of the US coastline. Many harmful tsunamis have occurred along the coasts of California, Oregon, Washington, Alaska and Hawaii.
A movement of the ocean floor, caused by earthquakes, most often causes tsunamis. If a tsunami occurs close to a coast, the first wave could reach the beach in a few minutes, even before a warning is given. Areas are at greater risk if they are less than 25 feet above sea level and within a mile of the coastline. Drowning is the most common cause of death during a tsunami. Tsunami waves are very harmful to buildings. Other dangers include floods, pollution of drinking water, and fires from gas lines.
An accurate prediction (预报) system will allow authorities (官方) to issue timely warnings and save lives in the event of a shore-bound tsunami. But forecasting tsunamis accurately is very difficult because the ocean is usually calm before they strike land.
65. What can cause tsunamis according to the passage? ( 回答词数不超过6个 )
66. What harm can a tsunami bring besides killing people and damaging buildings? ( 回答词数不超过15个 )
67. Why is it very difficult to forecast tsunami accurately ? ( 回答词数不超过9个 )