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Now listen to the following recording and answer questions 16 to 19.
16
A.There are different kinds of sound waves.
B.Different people have different abilities of sense.
C.There are different kinds of seismic waves.
D.The travelling speed of waves differs greatly.
17
A.They travel deep inside the earth.
B.They travel slow inside the earth.
C.They are too small to be felt.
D.They travel too fast to be felt.
18
A.The preliminary waves.
B.The secondary waves.
C.The surface waves.
D.The body waves.
19
A.The love waves.
B.The primary waves.
C.The surface waves.
D.The Rayleigh wave.
