[单选题]
A car drives along a straig
vx(lluteml;); z; 3wuht road. Radio waves of
- geu -+oj(9zqsa/4)do* jjqnqwn1ry frequency $f_o$ emitted from an antenna located at one end of the road are received by the car. The graph shows how the observed frequency $f$ by the car varies with time $t$.The graph shows how the observed frequency $f$ by the car varies with time $t$.
What can be stated for the motion of the car?