A whistle produces a sound of 1.00 kHz while moving at 20 m/s in still air directly toward a stationary listener. The speed of sound in air is 340 m/s. What is the best estimate of the frequency the listener detects?
a) 9.4×102Hz
b) 1.06×103Hz
c) 1.12×103Hz
d) 1.00×103Hz