[单选题]
A sound source approaches a 3*o3 vk lk5vv4iao0bb stationary observer. The frepd2oup4bea*9g m1* h mquency heard by the observe m9*bua pdeomp 41h2g*r is
A. higher than the source.
B. lower than the source.
C. the same as that of the source.
D. equal to zero.
