单项选择题

When we speak，sound waves begin to travel and go in all directions．

A．当人们说话时，声音向四面八方传开。
B．当我们说话时，声音就开始传播，并且向四面八方传开。
C．当我们说话时，声波开始传递，而且向四面八方传播。
D．当说话时，声波开始旅行，并且走向四面八方。
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