Câu hỏi:

 Read the following passage, and mark the letter A, B, C, or D on your answer sheet to indicate the correct answer to each of the questions.   

   The Richter scale is a numerical logarithmic scale developed and introduced by Charles R. Richter in 1935 to measure the amplitude of the largest trace recorded by a standard seismograph one hundred kilometers from the epicenter of an earthquake. Tables have been formulated to demonstrate the magnitude of any earthquake from any seismograph. For example, for a one- unit increase in magnitude, there is an increase of thirty times in released energy. The Richter scale considers earthquakes of 6. 75 as great and 7. 0 to 7. 75 as major. An earthquake that reads 4 to 5. 5 would be expected to cause localized damage, and those of magnitude 2 may be left. It is estimated that almost one million earthquakes occur each year, but most of them are so minor that they pass unnoticed.

What does this passage mainly discuss?