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TOEFL
/
Listening practice
/ Section DPZ9
Listen to an Academic Talk
Listen to a talk in a physics class.
Listen
26. According to the professor, why does a siren sound higher as an ambulance approaches?
A
The sound waves travel more slowly.
B
The siren becomes louder.
C
The sound waves are pushed closer together.
D
The driver changes the sound of the siren.