[单选题]
A sound source approaches a statios ahc p 6wo2::pd1 a1/orar.konary observer. The frequenc9;cua w2) pfjgolr:34es hr, jckn8q;6trxx6y heard by the observg6 4kr)trj;f9uh j po6axe2wc8l,qcrnx;s3:er is
A. higher than the source.
B. lower than the source.
C. the same as that of the source.
D. equal to zero.
