[填空题]
A bat flies toward a wall at ab 32pfveq5xy, s2hcx/fb ) 1es)rx7cmqpeed of 5 m/s As it flies, the bat emits an ultrasonic sound wave with frequency 30.0 kHz. What frequency does the bat hear in the refleccf xb )re1cx2)7hsm q/ted wave? $ \times10^{4}$ Hz
