[单选题]
A light source approaches a stationary reef+cu49+ jujm ceiver 0x 5vn*3 gp.7 qxd8jcvaphz d1at an increasing speed. The frequency of the emitted light is constant. Which graph shows how the observed frequency f by receiver variesdgzva 8dvp0hcp75.3xj1qnx * with the speed v of the light source?