[单选题]
A car drives along a ay:9v9jre9h0vnz.y xfz)u i,p z)ad, straight.f6fvo.kb vfx,enx5us l5ha b,*uujr0g. ;y6 road. Radio waves of 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?
A. Stationary then approaches the antenna at a constant speed.
B. Moving at constant speed towards the antenna then stationary
C. Accelerates towards the antenna then moves with constant speed.
D. Accelerates towards the antenna then stationary.
