单项选择题


Questions 18-21 are based on the passage you are going to hear.
What is the use of a seismograph

A.It is used to record the strength of an earthquake or seaquake.
B.It is used to record the direction of an earthquake or seaquake.
C.It is used to reocrd the length of time of an earthquake or seaquake.
D.It is used to predict when a tidal wave will hit land.