12. You and your father inspect an empty house with the hopes of buying it. You walk
through the rooms talking to one another, and you notice that your voices and footsteps
are echoing in the big, empty house. What causes the echo?
a. sound waves reflecting off smooth, flat surfaces throughout the house
b. sound waves moving around the large rooms
c. sound waves moving slowly through air
d. sound waves refracting around corners in the empty rooms.
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