单项选择题

If someone holds a book 6 feet directly in front of Denis and then moves it only 1 foot directly in front of him, what change in sound does. Dennis hear

A．A lover-pitched sound.
B．A higher-pitched sound.
C．A sharper sound.
D．A softer sound.
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单项选择题
Bower believed Dennis would be the ideal subject for his experiment because ______.
A．Dennis was blind at birth
B．Dennis was younger than anyone else he could find
C．Dennis’s parents were quite worried about his future
D．Dennis always produced sharp clicking sounds with his tongue
单项选择题
How could Dennis distinguish between a small ball and a large ball from a distance of 3 feet The large ball would produce ______.
A．a sharper sound
B．a softer sound
C．a higher-pitched sound
D．a louder sound
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