[填空题]
A bat at rest sends out ul;bs *uwmf (g/:joyw g2pm;a a(trasonic0;(+vembrfc b sound waves at 50.0 kHz and receives them returned from an objevf( bce;0+rmbct moving directly away from it at 25 m/s What is the received sound frequency? $ \times10^{ 4}$ Hz
