[单选题]
A light source approaches a statioyesayo ) 9o;6b6)lxl bnaq 1ds2b7d gv.r: 1qsaqry receiver at an increasing speed. The frequens1 bd v:1gqrqa27q. dscy of the emitted light is constant. Which graph shows how the observed frequency f by receiver varies with the speed v of the light source?
