Every year there are hundreds of earthquakes in different parts of the world. In September, 1923, Tokyo and Yokohama were both destroyed by an earthquake and the fires that followed it. They had to be completely rebuilt. One of the most serious earthquakes was in China's Shanxi province in 1556. It killed almost one million people. We measure an earthquake's strength on the Richter Scale. The Richter Scale was introduced in 1935 in Southern California in the USA. It measures earthquakes on a scale of one to ten. Any earthquake measuring five or more is usually serious. The Earth's crust  is made up of rock called plates. As these plates move, they sometimes crash against each other, causing the crust to quake. In cities such as Tokyo, where small quakes happen quite often, many modern buildings are designed to be flexible so when the Earth moves, they move with it. Earthquakes can also break up gas and oil pipes. This can cause fires to break out, which can do as much damage as the earthquake itself. Another effect of earthquakes is _ These are huge waves created by earthquakes beneath the sea. They can be many meters high and cause great damage to coastal towns and cities, China, Japan, Russia and the USA have the highest occurrence  of earthquakes in the world. The passage is mainly about  _  .
scientists who study earthquakes the way of measuring earthquakes a usual natural disaster what people should do in the earthquake
Question: Every year there are hundreds of earthquakes in different parts of the world. In September, 1923, Tokyo and Yokohama were both destroyed by an earthquake and the fires that followed it. They had to be completely rebuilt. One of the most serious earthquakes was in China's Shanxi province in 1556. It killed almost one million people. We measure an earthquake's strength on the Richter Scale. The Richter Scale was introduced in 1935 in Southern California in the USA. It measures earthquakes on a scale of one to ten. Any earthquake measuring five or more is usually serious. The Earth's crust  is made up of rock called plates. As these plates move, they sometimes crash against each other, causing the crust to quake. In cities such as Tokyo, where small quakes happen quite often, many modern buildings are designed to be flexible so when the Earth moves, they move with it. Earthquakes can also break up gas and oil pipes. This can cause fires to break out, which can do as much damage as the earthquake itself. Another effect of earthquakes is _ These are huge waves created by earthquakes beneath the sea. They can be many meters high and cause great damage to coastal towns and cities, China, Japan, Russia and the USA have the highest occurrence  of earthquakes in the world. The passage is mainly about  _  .
A. scientists who study earthquakes
B. the way of measuring earthquakes
C. a usual natural disaster
D. what people should do in the earthquake
Answer: