[单选题]
Suppose that a sound b79/zrq*yarq 1ebrk 0so3f ly68wqciv 6r.vrw *urce is emitting waves uniformly in all directions. If you move to a point twice as far away from the source, the frequency of the so3w8.i c q6wry 6r*lvfvund will be
A. unchanged.
B. half as great.
C. one-fourth as great.
D. twice as great.
